Hi,
Just wanted to let you know that I also just experienced this exact
issue with Ardour and a Cakewalk (Roland) UA-25 EX card.. Thanks to
your messages, I gave a try to jackd v1 and could finally export my
project. I don't know if it can be related, but that did not ever
happen with Kubuntu 11.10 and earlier versions (I now run Kubuntu
12.04).
Regards,
Loris