Good news are, your shield is connecting OK to the network and you can procceed with the examples.
Only bad thing is that gsmscannetworks is not running properly in your environment... Following your post, it looks like gsmAccess.begin() is not giving an answer in gsmscannetworks. The funny thing is that gsmAccess.begin() runs OK in TestGPRS.
I've found something that can be improved in the network scanning code but your sketch doesn't even reach that point...
I'll ask you a couple of things:
- Have you left gsmscannetworks running for at least a couple of minutes?
- May you copy a dump of gsmscannetworks?
Have you tried any example?