404 errors - pages sought in wrong dir.
 

I have been using UDM for several years, successfully. One issue that has long puzzled me that may be UDM related is that my error log script (404helper.cgi) frequently reports 404 errors on pages that do exist but that are being demanded in the root directory. For example the file /support/sponsorship.htm does exist but the 404 error relates to the file /sponsorship.htm as if it were in the root directory. I don't get to know where the error is coming from.

I am pretty sure there are no incorrect links in the menu structures.

Does anyone think this is related to UDM?

Run your site through Web Link Validator. This will show you if you have any broken links on your site, and should tell you whether your problem is UDM related or not.

I agree. I'd double check the site with a link validator. One issue I see is people use relative paths in their links on the udm menu, which might cause bad links.