This started happening to me today. Some facts:
1. There is no CD. I created two files from scratch within Word (Office 2007 SP2, fully licensed). I saved them under the names I wanted. I occasionally used the "Save" icon to save my changes. At different times, both files suddenly refused to save and gave the (Read only) tag in the title bar.
2. The properties box still shows "Read only" as UNCHECKED. The properties are not editable.
3. It has now happened twice for one of the files; I'm on the third different file name.
I had never seen this problem before in years of use.