Here's a thread from vbulletin.com where someone had the same error:
https://www.vbulletin.com/forum/show...this-directive . It basically says to try disbaling plugins until you identify a mod that's causing the issue.
I don't know why that would start happening when you change hosts. I googled the error and it seems like it may have to do with Apache SSI module, so maybe you have a different server configuration at your new host.