This can be caused your firewall. Disabling and rebooting can sometimes alleviate the issue, but some firewall software must be uninstalled instead.
Outpost Pro will cause this issue with high CPU traffic. Excluding µTorrent from its rules can help.
Avast is known to cause this issue with a feature called P2P shield. Disabling this feature will solve the issue.
Spyware Doctor 5 causes µTorrent to freeze when installed. The only fix is to uninstall it, or roll back to version 4 of Spyware Doctor.