I encountered a problem recently where users were reporting that documents they were working on in Word 2007/2010 were randomly becoming read-only and preventing them from saving changes. Initially, I was skeptical to this, and rather assumed that a certain subset of the documents were actually marked read-only for some reason. That being said, my first thought was that someone flipped the “Read-Only Recommend” flag on the document, which would not only cause the document to open read-only, but also cause any other files created from that original document to be read-only as well. Not to go off on a tangent here, but you can check to see if this flag is on a document through the Save-As dialog in Word, under Tools\General Options:

To my dismay, one of the example documents the user provided was not marked with this switch, and furthermore, I (and the user) could open the document and re-save it without any problem.

To make a long story short, the document did not open in read-only mode, however at some point during the session (even with a few intermediary saves in between), the document just magically becomes read-only an prompts for a save as. After a lot of searching around the web, the workaround for this problem is to disable the “Allow Background Saves” under the Save category of the Advanced Options in Word.

Despite what you would assume, this feature doesn’t have anything to do with the autosave feature, but rather determines if save operations occur in the foreground or background. With this setting disabled, you will need to wait for Word to finish any save processing before being able to continue typing or working with the document. This really isn’t a big deal, and you would probably only notice a delay when working with very large files.

So far, the problem has disappeared.