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. Basically, it's stating the computer program is making an illegal request.

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 you are receiving an Illegal Operation when running a game or program it is recommend that you temporarily remove or disable programs running and TSR's running in the background, ensuring that these programs are not causing your issues.

If, after removing these programs, you run the program or game and no longer receive the Illegal Operations, it is recommend that you reboot the computer and disable or End Task each program or TSR one at a time to attempt to determine what 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 programs life cycle.

Data 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

If running a program or game onto a hard drive 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 that is used to obtain more memory or handle the computer memory in replace of Windows, it is recommended you temporarily disable or uninstall this program to verify it is not the memory manager causing the Illegal Operations. 

Bad, incorrect or not the latest video drivers

Bad, incorrect or not the latest video drivers may cause Illegal Operations when performing such tasks as moving the mouse or dragging data from one source to another as 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 is loaded into memory and can change the data of program files when infecting a computer, make sure an anti-virus protection utility is installed on the computer and that it is up-to-date.

Added hardware

If added hardware has been recently installed onto the computer it is likely that either the hardware is conflicting with other hardware devices on the computer or that the drivers used to install that hardware is causing issues with other hardware or software installed on the computer. This is especially true with computer memory upgrades.

If added hardware has recently been added to the computer, temporarily remove that added hardware and the software associated with it to make sure it is not causing the problems.

Corruption or problem within Windows

Because Windows controls the memory operations as well as the file structure and association, it is possible for Windows or files associated with Windows to become corrupted, causing Illegal Operations or other errors. If you've tried all the above suggestions we suggest trying to reinstall Windows.   

Bad Memory, invalid bits or physically bad memory

It is possible that bad memory can cause Illegal Operations. If you have recently added memory to the computer, it is recommended that it first be removed to verify that you are not experiencing conflicts with the recently installed memory. If no memory has been recently added to the computer and you have tried all the above recommendations test your computer memory.

Additional information

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