I had errors with using the upgrade database feature on advanced install migration also at the check database stage. Mine simply just didn't do anything when I clicked and couldn't proceed. Tried other work around and got 503 error. What finally worked for me was the traditional approach. Moved the site files and putting them in their locations/folders same as it was on old server. Creating the new database. Uploading the sql file. Manually go through the main config file in core/config and updating all the links and info. Then put the setup folder in for the version and run just a normal update. Will have to specify the location of the core and a key if you changed it. Went off without a hitch! Finished with copying new install for advanced into the core and setup and running it one more time for good measure. Would have ran version upgrade instead at that point but didn't need it.
MODX...the Zen of CMS
"Bight off more than you can chew and keep right on chewing."
The advanced distribution just won't work on some servers.