"or is it because I've changed from a different firm"

Yes, if you have a new firm you need update your EFIN and send a copy of that EFIN application to Intuit for it to be reflected on your program. EFINs are assigned to a firm, not to a person.

Did you get a new EFIN when you changed firms? 

You may want to reach out to IRS EServices and see what needs to be done, once you have a new EFIN Summary Applicaiton you can follow the instructions here to get that to Intuit.

Register and Manage your EFIN with Intuit before e-filing