Quick: Set .bak file for that drawing to all inherited rights and be sure it is not read only.
Very strange problem showed up. Engineer trying to save a AutoCAD drawing got the following error message:
Saving as any other name works fine but every time he tried to save as that name it removed both the .dwg and .bak files and saved the file as .tmp file.
Verified this behavior on 2 different machines.
Found a link to some information that was helpful stating at the end that the .bak file might be read only.
I check and the .bak file was not read only, but when I right clicked the file and checked the security settings for the file it was not inheriting security from the folder. I set the .bak file to inherit security and now it works.
Still odd because I would think that with the .bak file coming and going it would get the correct security but not the case for some reason.