These are user to user forums (none of us works for the vendor) and it sounds like you'll need hands on support to continue; the vendor support can be reached through the Support Desk

There is the occasional host that just won't work with any product due to security issues, such as NameCheap.

There are also PHP Version Compatibility issues if you're attempting to run v8 on a PHP7 system for example; have you run my "UBB.threads System Requirements Test" script?

I am a Web Development Contractor, I do not work for UBBCentral. I have provided free User to User Support since the beginning of these support forums.
Do you need Forum Install or Upgrade Services?
Forums: A Gardeners Forum
UBB.threads: UBBWiki, UBB Styles, UBB.Sitemaps
Longtime Supporter & Resident Post-A-Holic
VNC Web Services: Code Modifications, Upgrades, Styling, Coding Services, Disaster Recovery, and more!