A 500 error is a generic error code.
Server logs if accessible would be more specific.
If absolutly nothing has changed on your site.
Meaning modifications to the script,changes in the ubb console.
then I would suspect the host provider has changed something like upgrading apache , php , etc ad possibly some settings are now incorrect.
You have the current version I would start with the landing page of ubb cp.
See if it reports any issues to address.
The scroll down to the bottom and check permission checks.
to see if you have any failed file/folder permissions.
Other than that contact your host to resolve your issue, They can provide more specific error info.
