Hi Mats, and welcome to Isolator!
The error message you received means the recording block (inside the using statement) could not record any calls - this may happen when the calls inside the block are from mscorlib.dll (which Isolator cannot control), which does not seem to be the case here.
I suggest we take this case offline - I will send you an email from our support account and ask for more details so we can recreate the issue locally.
Thanks,
Doron
Typemock Support