Mountain Lion upgrade install can be a real mess. Whatever others might say the networking goes to pot.
Are you using wireless? That is worst affected.
If you are not already plugged into the TC by ethernet do so.. isolate the computer and the TC entirely from the network.. ie turn off wifi in the computer.. only one lan connection on the TC to the computer.
Do a full factory reset.
Use the airport utility 5.6 since you have it from the upgrade.. and setup the TC with all SMB names.. short, no spaces, pure alphanumeric.. this is important for ML.. it doesn't handle names with spaces at all well.
TC name, Wireless names.. hard disk share name.. all must be SMB type.
For wireless use WPA2 personal security.. passkey 8-12 characters.. pure alphanumeric.. no spaces of course.