Sudden problem with php error

We had a site running the CMS, and then needed to change servers. Both old and new were similar environments, but the old was Plesk 9 and the new is Plesk 10. After migrating the site over, there is an open_basedir restriction error that comes up. Nothing else changed. Just for kicks, we turned ON PHP safe mode, then turned it OFF again to see if that would help reset anything, but it didn't.

Here is the error at the header of each page:

Warning: is_dir(): open_basedir restriction in effect. File(/var/www/vhosts/sitename.com/httpdocs) is not within the allowed path(s): (/var/www/vhosts/sitename.com/httpdocs/:/tmp/) in /var/www/vhosts/sitename.com/httpdocs/cmsAdmin/lib/init.php on line 173

Our hosting support offered to disable PHP open_basedir protection, but I don't think that's the answer and feel something else is happening with the configuration.