Is your OS "windows"??

there is a "who-do vodoo" that happens when you have you folders open with "show thumbnails" and having the file open in PS. Microsoft's Explorer (not the browser but the window explorer) fails to release the file so PS looks at it as "being in use", this causes that whole run-around of "you can't save it cause it's open, but of course it's open, I'M TRYING TO SAVE IT!!!!". Microsoft won't admit to the issue and feels it's Adobe's problem...

best thing is not to use the "thumbnail" feature... :) retrocity