maybe this thread will help you, ask Arvixe to disable 32 bit on the application pool, it seems to cause problems on Arvixe servers
though I also still have doubt about your install process and whether extra files are deployed such as temporary files leftover from extracting on the server. I don't trust any web control panel file manager. I extract locally and upload files directly by ftp
downgrading any version of mojoportal is always problematic, in some specific cases it can work if there is not much difference between versions but generally if a site has a newer version installed, going back does not change the newer schema changes and the old code may not work with the newer schema, the only time its ok is if there were no schema changes between the 2 versions.
no-one else is reporting this problem so it does not seem the problem is intrinsic to the mojoportal package, it is some strange deployment problem in my opinion