I'm getting this right now too. Installing it to my 😄 Driver as opposed to my S: Drive doesn't work, running as administrator doesn't work, I have the most up to date version of Microsoft Net Framework, and I have the Ultima PSOBB folder added as an exclusion in Malwarebytes. IS WHAT I WAS GOING TO SAY
If you are getting this error like I was, check to see if your malware software already has psobb.exe quarantined. Adding the folder to an exclusion unfortunately doesn't automatically restore quarantined files. If you are also using Malwarebytes like me, you also have to add an exclusion for the website "ultimapsobb.com" and then it will stop giving you the error. After all that it works for me now.
