Are you trying to clear out old error messages displayed in the Web GUI? In that case you may want to try the "mmhealth node eventlog --clear -N node[,node2,...]" command for the node(s) where the error was reported. Be advised though that you will lose the entire event log for those nodes, not just the old entries.
Not sure if Zimon has a role to play with any of that.
------------------------------
Regards
Florian
------------------------------