Microsoft outlook

I am running LTM 11.5.2 with f5 Iapps f5-microsoft_exchange_2010_2013 v1.5.0 it was working for awhile and now some users are having connection issues. to the outlook client getting error outlook not available. pcaps look good on client side. took pcap on ltm side still looking thru so far nothing. Microsoft network monitor shows EPM protocol error response message Ep_s_not_registered . has anyone seen an error like this.