I just discovered the same issue on a brand new install of Veeam and the server that was backed up.
"4/9/2015 4:14:40 AM :: Unable to truncate Exchange transaction logs. Details: Cannot finish snapshot: no job found. "
This new server does not have exchange on it - it's a new file and print server. This is the very first backup, and the only backup so far at this site, so the log file I submitted is pretty small
Support ticket is:
I did a test restore of a file so the backup itself is good, but this should help identify the phantom exchange error.