I think the problem is that the server does not send the realm in digest md5 step1.
Try to fetch and compile the latest sources. This should be fixed there.
sorry, but I don't see why it would fail from the logs.
I assume you would have to ask nimbuzz if they have changed anything on the server. If yes we need more info on the details.
I see no differences between the success and failure logs.
You can try yourself, maybe you see something, just base64 decode the value of the challenge and response xml tags and you get the Raw Sasl messages.