I know this is an old thread, but I just had the same problem and wanted to comment.

My issue was with opening an Excel file. It appears that it doesn't matter what file type is being opened, however.

Same problem as described. Multiple years of opening the file via Outlook and suddenly a problem. Other solutions on the internet point to Antivirus problems, or having Excel "ignore other applications". Neither are correct for this specific error message.

The root problem is in opening files with the same name repeatedly. Outlook temporary file naming conventions will rename the temp. file with a (##), up to ## = 99. At the 100th iteration of opening the file, you will receive the "folder permission" error. This is why the fax view crashed as well, because they typically export always as the same name file too.

The solution proposed above in this thread - deleting the temporary folder contents - is correct and successfully solved my issue. However, note that, depending upon your Outlook version, the sub-folder under Temp. Internet Files will be OLK or OLK1, etc.