That's the only thing on my conscience. Installed the new one without removing the old one (the new one seemed perfectly happy about it after a query) but then saw the instruction to remove the old one first so I removed the new one and reinstalled again.
If this is likely to be the problem can you advise me how to manually clean things up and start again if that's the best thing?
The redundant file management/uploader extension has been removed.
Since writing the above I thought I'd use my Mac Time Machine to restore things to before I started so I could remove the old extension as instructed. I restored Application Support/Adobe, Apps/Dreamweaver, and Apps/Extension Manager, but Universal Email 4 is still showing in the restored Extension Manager. Really can't think of what to do now.