I've read other solutions, but my problem is slighlty different. Problem occurs in domain environment. We work in a subdomain, but we also have some employees coming with notebooks registered in top level domain. Our internall policy enforces them to logon their laptops with our special guest users accounts firstly, then they have access to our citrix web interface. This was working untill Windows 7 appeard (on Xp we had no problems at all). When we try to logon with such a user (of course using convention domain\user, but also fqdn\user), we get after a while error message saying:
"There are currently no logon servers available to service the logon request"
We played a bit with network settings, like adding dns suffixes for all subdomains, but, without any result. It looks like system has no problem with resolving names of our domain controllers. There are no connectivity problems. Moreover, there are no coresponding events in event log (system, app, security), like wouldn't anything happened. At the same time, they are able to logon with their originall main-domain users without any problem (however now i think that this might be also a false assumption, because they have cached credentials already)
Just a thing to add - trusts are set bi-directional. Normally, our users are able to logon on top level domain servers. So this shouldn't be releated to trusts.