This morning I opened an older PP deck that I had in order to update the branding. I then closed it and re-opened to confirm that the file looked right before emailing it out.
It opened with the Read-Only statement showing in the title bar and even though I did want to make a simple change (resetting the saved deck at Slide 1 instead of Slide 12).
I could not save as I got an error with the Read Only flag. The error within Powerpoint stated that the file was in use on the network or words to that effect. Trying to save over the top of the existing file gave another error that the file was already open in Powerpoint, which suggested to me there two Powerpoint instances.
My fix was:
1. Close Powerpoint.
2. Open Task Manager (Right click task bar -> Start Task Manager) and under the Processes tab
3. Look for a Powerpoint process and select End Process (click ok to kill it as you are the only user – right?)
4. Reopen your file in Powerpoint
Seems that Powerpoint is holding the file open with an incomplete process when the app is closed. This means the most recently used file is flagged as still in use by that process and opening the file again is done with a read-only process as a result.
For the record this is Windows 7 x64 with Office 2010