How do I fix illegal operations?

When the operating system or computer processor receives an instruction from a program that it does not recognize and cannot process, it may issue a command known as an Illegal Operation. Below are reasons why an Illegal Operation happens on a computer.

Illegal Operation

TSR's or third-party programs

TSR's or third-party programs running in the background are one of the more commonly found reasons for Illegal Operations. If the Illegal Operation is happening when running a game or program close all other open programs and TSR's running in the background.

If after removing these programs you no longer receive the Illegal Operation messages, we recommend that you reboot the computer. Once it's up, disable or End Task each program or TSR one at a time to determine which program is causing the Illegal Operation.

Error in program coding

Verify that the program causing the Illegal Operations is compatible with your version of Windows and check with the developer to make sure no patches or updates are available. There is no such thing as a perfect software program, and it is not uncommon for multiple patches and updates to be released during a program's life cycle.

Data is not being read properly from source

When running a program or game from a CD you receive an Illegal Operation, verify that the CD is clean. Additional information on how to clean a CD or CD-ROM drive can be found on our Cleaning Page.

If you are running a game from a floppy diskette or other drive make sure the disk or drive does not have physical errors with it by running a ScanDisk.

Installing a program or game on a hard drive that has errors or is highly fragmented

Make sure that drive is not fragmented or corrupt by running ScanDisk and Defrag on the drive.

If errors exist on the hard drive, they cause the program or game to run improperly and can cause Illegal Operations.

Corrupt files

Corrupt, bad, or missing files can cause Illegal Operations. Try uninstalling and then reinstalling the program causing the Illegal Operation to verify that any corrupt, bad or missing files are replaced or repaired during the reinstallation.

Memory managers

If you are running a memory manager, it is recommended you temporarily disable or uninstall this program to verify it is not causing the Illegal Operations.

Bad, incorrect, or outdated video drivers

Bad, incorrect, or outdated video drivers can cause Illegal Operations when moving the mouse, highlighting, or when high demands are placed onto the video card. Try decreasing the resolution to make sure your current settings are not causing the problem.

If after adjusting the video settings you still encounter the same issue, verify the computer is utilizing the latest video card drivers by visiting our computer video drivers section.

Computer virus

Because computer viruses and other malware load into memory and can improperly modify files they can cause Illegal Operation error messages. Make sure an anti-virus protection utility is installed on the computer and that it is up-to-date.

Added hardware

If new hardware has been recently installed (e.g. computer memory) in the computer it or any drivers that had to be installed may be conflicting with other computer hardware. Temporarily remove any new hardware and the software associated with it to make sure it is not causing the problem.

Bad Memory, invalid bits or physically bad memory

Bad memory can cause Illegal Operations. If you have recently added memory to the computer, remove the memory to make sure it is not causing the problem. If no memory has been recently added and you have tried all the above recommendations, test your computer memory.

Corruption or problem within Windows

Because Windows controls the memory operations and all system operations if any part of Windows is corrupt it can cause Illegal Operations. If you have tried all the above suggestions, we suggest reinstalling Windows.

Additional information

  • See our Illegal Operation definition for further information on this term and visual example of the error.