It doesnt really state what the problem is here, aside from a program error. It's always a good idea to save often. And you mgith also check to see if auto-save was on and perhaps saved a version of your project?
Otherwise I would recommend quitting and restarting Photoshop to solve the problem, or restart holding down Command+opotion+Shift (ctrl+alt+shift on pc) to remove the preferences which can also sometimes get corrupt.
hope that helps,
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