SuperMemo errors are grouped in:

• fatal errors - (red color) most dangerous errors that can compromise the integrity of your learning material
• learning process errors - (yellow) errors that indicate problems with the learning process 
• local errors - (yellow) errors that are less severe and may damage single elements in your collection
• warnings - (white) errors that may be ignored

See Error FAQ for the list of all errors that have ever been reported to occur in SuperMemo. If you receive an error that you cannot interpret or is not explained sufficiently, write to bugs(AT)supermemo(.)com

Fatal errors

If you get any of fatal errors listed below, do the following immediately:

1. backup the entire collection with File : Copy collection
2. run the recovery procedure with File : Repair collection
3. if your collection still displays errors after Repair collection, write to bugs(AT)supermemo(.)com (please retain your material for possible submission via e-mail)

This is the list of most dangerous fatal errors:

1. Total<Pending - your KNO file has been fatally damaged. Please report this problem to bugs(AT)supermemo(.)com!
2. Total<Memorized - your KNO file has been fatally damaged. Please report this problem to bugs(AT)supermemo(.)com!
3. Writing beyond HugeArray allocation - SuperMemo uses THugeArray type to store various forms of large arrays of information (e.g. item subsets). This error indicates a severe damage to such structures that is extremely dangerous to the integrity of your learning data
4. Reading from beyond HugeArray allocation - SuperMemo uses THugeArray type to store various forms of large arrays of information (e.g. item subsets). This error indicates a severe damage to such structures that is extremely dangerous to the integrity of your learning data
5. Cannot swap HugeArray memory to disk - SuperMemo uses THugeArray type to store various forms of large arrays of information (e.g. item subsets). This error indicates a severe damage to such structures that is extremely dangerous to the integrity of your learning data
6. Cannot reload HugeArray from <filename> - SuperMemo uses THugeArray type to store various forms of large arrays of information (e.g. item subsets). This error indicates a severe damage to such structures that is extremely dangerous to the integrity of your learning data
7. Wrong component buffer marker - file with component information (compon.dat) has been damaged and may result in loss of information from individual elements (most frequently, all components will simply be deleted). You must immediately proceed with verifying the integrity of the collection. Have a closer look at your hardware (esp. reliability of read/write operations of your hard disk)
8. Cannot read data for element

Learning Process Errors

Errors listed below affect the correct execution of your learning process. They do not compromise integrity of your study material; however, they can ultimately lead to a breakdown of the process in which the model of your memory is built and used in scheduling repetitions. If these errors occur, backup your collection and run File : Repair collection with Basic recovery checked

1. UsedInterval<1 in GetRepetitionData - this happens if the learning algorithm finds an element whose last repetitions was made "in the future" (i.e. on a date that is later than today's date). This is most likely a result of using SuperMemo with your date wrongly set in your computer. Important! You should never play with the date to delay repetitions, do repetitions in parts, apply Mercy to a subset of outstanding material, etc. SuperMemo must work with the date set correctly! This is reflective of your learning process and how your memories get consolidated in time.

Local Errors

Errors listed below are less severe and are more likely to be local (i.e. affecting only one or more elements). Once you encounter such errors, it is still recommended that you:

1. backup the entire collection with File : Copy collection
2. run the recovery procedure with File : Repair collection

Local errors:

1. Empty RTF text found at registry member <member number> - this error indicates that a rich text registry member is associated with rich text that is empty. This should not occur in normal circumstances and may indicate a damage to your text registry. Review your text registry, your collection, make a backup and run Repair collection with Rebuild registries checked
2. Cannot compute repetition results - this error should not occur in normal circumstances. It is not dangerous to your data but it may indicate some serious instability of your Windows or SuperMemo itself. Recommended action: restart Windows and run Repair collection (Basic recovery)
3. Parent=nil at MakeVisible changed to Parent=1 - there is a discrepancy between the displayed structure in the contents window and the knowledge structure stored in SuperMemo. Try restarting SuperMemo  
4. MMSYSTEM277 A problem occurred in initializing MCI. Try restarting Windows - this is a Windows problem. MCI stands for Media Control Interface and is used by Windows to handle multimedia. MCI functions are called when processing sound and video. However, GIF images processing in SuperMemo may also invoke the function timeGetTime(). If restarting Windows does not help, you may need to reinstall your MCI subsystem. Often, reinstalling your sound board drivers helps resolve MMSystem issues
5. Cannot get the current Contents selection - if this error is followed by Access violation at address ..., the TreeView object in your Windows must have been corrupted (in memory). This is most likely a transient problem and could be remedied by restarting Windows

Warnings

These errors can be ignored or are easily resolved:

• Access denied! System locked by another SuperMemo - SuperMemo will display this message when KNO is locked by another instance of SuperMemo or if the KNO file is set to read-only (e.g. after copying from CDR backup). Remove the read-only status, quit other SuperMemos, at worst, restart Windows
• Element does not belong to the indicated category - this error is likely to occur in the first recovery executed on a collection upgraded from earlier versions of SuperMemo. It is harmless and comes from stricter category registration in SuperMemo 2000
• Error running SuperMemo - most likely this is an error generated by one of Windows modules while executing one of API calls from SuperMemo. This error is not likely to be of much significance. It may, however, indicate some instability of your Windows installation (e.g. incompatible drivers, older DLLs, errors in registry, etc.). This error is by far less likely to occur in Windows NT 4.0 and is mostly reported in old Win95 installations
• Non-zero category number in a template - this error is likely to occur in the first recovery executed on a collection upgraded from earlier versions of SuperMemo. It is harmless and comes from the fact that category information is not permitted in templates in SuperMemo 2000
• Primary storage file: <file 1> occludes secondary storage file <file 2> - secondary storage file is not visible due to an occluding file kept in the primary storage. If you want to restore the visibility of the secondary storage file (e.g. on CD-ROM), delete the file from the primary storage. This can happen if you edit files stored on CD-ROM (the edited copy is stored in primary storage). In SuperMemo 99, this warning would also erroneously be displayed if the collection path was forcibly set do a different case e.g. c:\SM99\systems\ in place of c:\sm99\SYSTEMS\. This could happen by running sm99.exe with a collection path as a parameter string
• Removing a reference to a deleted registry member - this error is likely to occur in the first recovery executed on a collection upgraded from earlier versions of SuperMemo. It is harmless and comes from stricter deleted registry member verification in SuperMemo 2000
• Template registry access error! Prohibited access - Position=<Pos1> - LastPosition=<Pos2> - except for situation in which this error might indicate an error in a template registry, this error is also likely to be reported in collections upgraded from earlier versions of SuperMemo (including collections published in SuperMemo Library). If a category uses a deleted template for tasks or topics, earlier versions of SuperMemo would just ignore it. SuperMemo 2000 reports it as an error and replaces the template reference with 0 (i.e. "no template"). In such circumstances, this error should be reported only once and should have no side effects or harmful consequences
• Wrong A-Factor distribution - the statistics of A-Factor distribution are inconsistent. This error can be ignored in upgrading from SuperMemo 98 or earlier to SuperMemo 99 or later
• Wrong Interval distribution - the statistics of interval distribution are inconsistent
• Error processing escape code

See: Error FAQ for the full list of known errors that may occur