If you were accessing this document using document CAL earlier then check again if your document cal assignment has been revoked. Such messages appear in this case as well. Besides that if this app works with section access then may be your permission from section access list has been removed.
After running into this problem myself, I figured that this happens if you save a .qvw document after doing a Limited Load from the Debugger and saving the file before doing a full reload. I have not found a way to reopen the denied/locked file. Had to go to a backup copy.