It looks like Teiid 9.0.1 is fine after all. The problem was that our API was redirecting to https and since we don't have the ssl certificate set up on the server yet the response was unreadable.
I believe we can put this one to bed. I'll mark Ted's answer as the correct one.
Thanks all for your help.
PS: Just to answer my own question, the setup we used is:
- JBoss 6.0 Community version
- Teiid 8.9.1 Runtime
- Teiid Designer Tools 9.0.1
That's great Vagos.. FYI - error handling/messaging has been improved for TD 9.0.2, so you would have received a better error message to help diagnose the issue more easily.