Today I upgraded all my exchange servers to CU3. All of them went well except for one. The transport service started and stopped after 1 minute and would log 3 event errors straight after each other:
The main error was complaining about one of my custom connectors. After that error another error 7001 logged with a TCP/IP error.
I removed the custom connector that worked on CU1, CU2 and CU2v2 and started the Exchange Transport Service, this time it started and did not log any of these errors again.
Hope it helps