|Oh yeah, if you didn't do the uninstall from add/remove there will be all kinds of remnants left.|
I assume the 'common files' folder has a separate folder in it dealing only with autocad and that's the one you're trying to delete?
Since you're trying to delete an entire folder, it's possible the folder is not read-only but some of the files in it are. You may need to go through the folder file-by-file and delete what you can and then check the attribute on anything that won't delete. You should also enable the viewing of hidden files. To do that, open 'my computer' and choose 'tools' from the toolbar. Then 'folder options', 'view' and under 'hidden files and folder' check 'show hidden files and folders. Then 'apply' and 'OK'. That way you'll be able to see all the files.
Some other things:
When you checked, was the 'read only' attribute set? If so maybe it reset when you booted to safe mode. Try safe mode again and check the attribute. Make sure it's not enabled and then see if you can remove the folder.
Also, run MSCONFIG and click the 'startup' tab and see if anything related to autocad is running. If so, uncheck it then 'apply', 'OK' and then I think you need to reboot. After it reboots run MSCONFIG again and see if it's re-enabled itself. Then try deleting the folder again.
If none of that works you could probably boot to 'safe mode with command prompt' and manually delete it using dos commands. But that can be tricky if you're not familiar with it so try all the other stuff first.