Perch Compatibility Test

Hi, this is a first for me...

Built the website on our test server as normal. Client has their own server, not the norm, but didn't see any issues using it. Uploaded the files, database and the front end shows no issues and works perfectly.

Admin page loads, once you try login you get a blank white page / 500 error on chrome.

I was looking on the site for the Perch Compatibility Test but it doesn't seem to be available anymore. Has anyone had this issue, and knows how to fix it, or can anyone point me in the right direction of the Compatibility Test

Thanks