no updates through fast channel notifications

hi,

I have some MPs in my environment that aren't sending properly notifications to clients about updates available to install. when I have a look at bgbserver.log I find that:

ERROR: SQL exception when retrieve client certificate from DB. Exception: SQL Server Network Interfaces: Error Locating Server/Instance Specified [xFFFFFFFF]. ~~OLE DB provider "SQLNCLI11" for linked server "[dbserver]\sccm" returned message "Invalid connection string attribute". -2146232060 SMS_NOTIFICATION_SERVER 02/11/2016 06:11:09 5140 (0x1414)
 Can't verify signature in message without client certificate for client SCCM GUID:D588D9CD-89A4-4EF8-A4B1-17FE73E0E7E9 SMS_NOTIFICATION_SERVER 02/11/2016 06:11:09 5140 (0x1414) Invalid hook to be decoded. Authentication SMS_NOTIFICATION_SERVER 02/11/2016 06:11:09 5140 (0x1414)
 Failed to decode message body (<BgbSignInMessage TimeStamp="2016-11-02T06:10:52Z"><ClientType>SCCM</ClientType><ClientVersion>5.00.8239.1403</ClientVersion><ClientID>GUID:D588D9CD-89A4-4EF8-A4B1-17FE73E0E7E9</ClientID></BgbSignInMessage>) with message header (<Message><SourceType>SCCM</SourceType><SourceID>GUID:D588D9CD-89A4-4EF8-A4B1-17FE73E0E7E9</SourceID><Hooks><Hook Name="Authentication"><Property Name="PayloadSignature" Value="QH4mS68Q43uaiDt0+sdXmhqLZiL/pmMPv5O9Evo5SupKVXqTwEvoIqMUN5LMQ2Oq&#xA;b0VnWI4D2p8lPqb0vJlnVnn2LNbosMFBBa//rJEA1xNCTylaCdTGGook+tNicoRa&#xA;yBEaMaUJM7nRzw5Kzld6GIhOOgc/IB2KHJeMWlXGXhM="/></Hook></Hooks></Message>) SMS_NOTIFICATION_SERVER 02/11/2016 06:11:09 5140 (0x1414)
 Failed to process SignIn message from client 2002:95c1:a9c8::95c1:a9c8:50246. SMS_NOTIFICATION_SERVER 02/11/2016 06:11:09 5140 (0x1414)