Unknown Photoshop error

Hello, Could you give us more info: please post the contents of the Photoshop menu help>system info, so that we get to know your OS, its version, the exact version of Photoshop you are running, the date of the GPU driver, etc.

Try again saving from web. I think it works, if not then try removing the profile files (Users/Username/Library/Preferences). Then restart your Mac and then re launch your photoshop version. It will work.