The magic is used to differentiate old state file format (which started with number of services) from the new extensible state file format (starts with 0, which is the "magic" - older monit versions will always start with number > 0).
It seems that the user's statefile is probably empty, hence the error is returned.
The solution is simple:
1.) stop monit
2.) remove the state file: rm -f /var/lib/monit/state
3.) start monit (will create new state file)
Originally posted by Martin @ http://nongnu.13855.n7.nabble.com