Windows error code 256 usually occurs on PCs that have been infected with the Sdbot virus or a variant of this virus. The virus itself creates an invisible process. This process will close programs that you might use to diagnose or configure your computer. In addition, the virus may stop other applications from running and completely lock up your Windows operating system.
If you are able to run your anti-virus program, do a complete scan on all system disks. The results you will get from doing this are going to vary. It will depend on your anti-virus program and the definition files that you have on your computer as to whether the virus is completely removed or not. This virus has been around for a while and most PCs should have the correct definitions to remove this virus as long as definitions are being kept current.
As good as most major anti-virus programs are, some will not be able to remove the Sdbot virus. Microsoft recommends using their Malicious Software Removal Tool. You can access this tool at the following address: : https://www.microsoft.com/en-us/safety/pc-security/malware-removal.aspx. This tool should remove the virus and allow you to go back to normal PC use. Microsoft does have a manual process that you can perform to remove this virus, but the process is very lengthy and should only be attempted by people who have a lot of computer experience and who are unable to run the automated fix.
After you run the fix mentioned above, restart your computer and try to access the programs that were causing lockups on your PC. You should now be able to use all of your administrative programs without getting Windows error code 256 again.
TipFor more information, please see: How to fix System error #256