Cause : IO COMM comes when the drive is encountering issues communicating with another device over a fieldbus network.

The A2005 alarm code on your ABB ACS550 drive indicates a fieldbus communication error . This means the drive fieldbus communication has timed out.

Check for and correct: 

1. Fault setup (3018 COMM FAULT FUNC and 3019 COMM FAULT TIME). 
2. Communication settings (Group 51: EXT COMM MODULE or Group 53: EFB PROTOCOL as appropriate). 
3. Poor connections and/or noise on line.