I'm not trying to be obtuse, really. But I'm confused.
The 404 error indicates the testing server does not map to http://www.sogomusicms.com/public_html/_mmServerScripts/MMHTTPDB.php.
I opened FileZilla and looked on the site and found that PHP file at that location.
Back in Dreamweaver, in the Basic Server configuration dialog for the testing server, the Web URL is http://www.sogomusicms.com/public_html/
It seems to me that the testing server IS mapped properly, and I can't figure out what I'm doing wrong. The text following the 404 message is no help. Your advice to "make sure to use the proper URL for the Web URL in the testing server settings" is undoubtedly accurate, but I thought I WAS using the proper URL.
It's probably something forehead-slapping simple, but I can't see it. I really appreciate your forbearance.