Is it doing it on only that document? What about other documents?
If the former, it's possible the document was corrupted somehow. (This could be from anything from power sags to faulty computer hardware to viruses.)
No, it's all the files Even if I create a completely new document.
For example if I try to create a Solid color layer I get the error message and if I open a document that already contains a solid color layer I get the message "This document contains unknown data" and if I click to open it anyway the solid color layer is just empty.
Other things to try:
-Hold down Cmd + Opt + Shift while starting Photoshop, which should ask if you want to delete settings. Click Yes. (Note this will reset everything.) Try doing various commands and operations again.
-If that doesn't work, try an uninstall and reinstall of Photoshop.
Deleting settings didn't help, but reinstalling Photoshop did the trick. Thank you!