error: file exists but couldn't be open for reading

I tried to open a photoshop file while it was open in after effects and this error pops up. I am unable to do anything in after effects at this point. I tried clicking the okay button, closed down photoshop and tried to close after effects (but i am unable to do anything with after effects). i cant close down the computer without this program shutting down but the error wont go away. Even restarting the computer didnt work.