We have a customer whose Forms Services are suspending intermittently (around once a week.)  When restarting the service we are able to retry the process and they go through properly.  We'd prefer to not have them stop randomly though.   When checking the error log we see an LFF502 Error. 

Here is the text of the error log.

An unexpected error has occurred. [LFF502-UnexpectedError]

Details:
URL:
Error: UnexpectedError
Date: 8/16/2018 10:02:14 AM (Eastern Standard Time)
HTTP Status Code: 500
Business Process ID: 0
Business Process Name:

Stack Trace:
Caught exception: Laserfiche.Forms.CommonUtils.Exceptions.LFFormsException
Message: An unexpected error has occurred. [LFF502-UnexpectedError]

Inner exception: System.DirectoryServices.Protocols.LdapException
Message: The supplied credential is invalid.
   at System.DirectoryServices.Protocols.LdapConnection.BindHelper(NetworkCredential newCredential, Boolean needSetCredential)
   at System.DirectoryServices.Protocols.LdapConnection.SendRequestHelper(DirectoryRequest request, Int32& messageID)
   at System.DirectoryServices.Protocols.LdapConnection.SendRequest(DirectoryRequest request, TimeSpan requestTimeout)
   at Laserfiche.Forms.CommonUtils.FormsUserSyncer.LDAPHelper.<LdapConnectionSearch>d__15.MoveNext()
   at Laserfiche.Forms.CommonUtils.FormsUserSyncer.LDAPHelper.GetAllGroups()
   at Laserfiche.Forms.CommonUtils.FormsUserSyncer.RetrieveLdapGroupsFromProfile(LDAPHelper ldapHelper, cf_tenants defaultTenant, cf_roles participantRole, List`1 existADGroups, UserSyncReport syncReport)
   at Laserfiche.Forms.CommonUtils.FormsUserSyncer.RetriveLaserficheAccounts(IEntityContext appContext, DateTime currentTime, Int32 expiryLen, String primaryEmailAddress, RetrieveAccountType retrieveType, UserSyncReport syncReport, Boolean forceSyncAll)
   at Laserfiche.Forms.Routing.UserSyncer.SyncConsumerInternal()

Any idea what might be causing this to happen?