Photoshop not flattening layers or saving due to program error

I'm always working with all sorts of files for my job, but today I have been working on a couple of files, layering them, when I go to flatten image this notification is showin 'Could not complete your request because of a program error.'

And then if I go to save as a JPEG expecting it to flatten that way it is also showing the same error - that said it isn't happening on everything, but 90% of files.

If I open an exisiting PSD with multiple files, and edit some text and save that is working fine, just seems to be when adding new layers from another image. 

Any help would be appreciated, I have cleared the cache, preferences and un installed PS

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