Problem

Q_SENTINEL.out: 2013/09/25 15:38:06   sendMessage failed with status -901

Resolution

This error message is generated by a corrupted tracker.pmq file, this must be recreated.
Perform the following steps:
1. Stop Gateway.
2. Rename the file .../Gateway/run_time/data/tracker.pmq to .../Gateway/run_time/data/tracker.pmq_old
3. Run the command:
pelmon check_base -ra
4. Start Gateway.