ok, you are running a really old version of mojoPortal, 188.8.131.52 was released in September 2009. That version did not show the trust level.
that error is very clear, it is caused by NeatUpload which is known to not work except in full trust.
version 184.108.40.206 was shipped with full trust/neatupload enabled by default, but for those in medium trust we shipped a web.mediumtrust.config that had neatupload removed to disable it. this file could be renamed to web.config to make the site work in medium trust.
so my best guess is your host changed it to partial trust lately and now you are getting the known neatupload error
if you have the web.mediumtrust.config file you could backup your current web.config and try that renaming the medium trust one as web.config
it may solve this error but, there are greater concerns I would be worried about. There have been various security fixes over time and a your version is known to predate some important security fixes.
If this is an important site I would want to upgrade it the latest version if I were you. But you need to be aware of several issues upgrading from that old, I'd recommend hire the i7media guys on our hosting page to help you upgrade if you decide to do it, because they can help you solve the upgrade issues you will encounter. For example you need to be aware of the following:
the latest version requires .NET 4.5 hosting, your current version runs in .NET 3.5 or higher, so you can only upgrade if your hosting has been updated to .NET 4.5 or if your host can move you to a newer server with 4.5
also your current version may have supported ms sql as old as sql 2000, but the latest version of mojoportal only supports sql 2005 up to all the latest
also there are likely changes in the skinning system that will require fixes in your skin after upgrading
the i7media guys could handle all of that and any other issues that might happen, so you might want to contact them for a quote