Yes, in this case you would be best to try a full reinstall. However, there is no guarantee that Sage 50 (Simply Accounting) 2012 will run in Windows 11 as it was developed before Windows 11 was available for testing. You will require your Account ID (400xxxxxxxx), Serial Number as well as your Activation Code. Oncce you have re-installed you may need to update the file depending on which you were using, 2012.0, 2012.1, 2012.2 ? 

Thanks Alwyn, reinstalled and all is working.

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