System Center Configuration Manager 2012 R2 SUP Error

Strange one. I started getting loads of these:

“STATMSG: ID=6703 SEV=E LEV=M SOURCE=”SMS Server” COMP=”SMS_WSUS_SYNC_MANAGER” SITE=000 PID=2176 TID=4892 GMTDATE=Mon Jul 28 00:00:07.224 2014 ISTR0=”Microsoft.SystemsManagementServer.SoftwareUpdatesManagement.WsusSyncAction.WSyncAction.SyncWSUS” ISTR1=”UssCommunicationError: WebException: The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel. —> System.Security.Authentication.AuthenticationException: The remote certificate is invalid according to the validation procedure.~~at System.Web.Services.Protocols.WebClientProtocol.GetWebResponse(WebRequest request)” ISTR2=”” ISTR3=”” ISTR4=”” ISTR5=”” ISTR6=”” ISTR7=”” ISTR8=”” ISTR9=”” NUMATTRS=0″

When synching my test SUP with WSUS. Found loads of stuff on the web about checking up on the SSL certificate assigned to the WSUS/ SUP site, checking the permissions on the ApiRemoting030 etc. Nothing worked. Turned out I’d changed its synch point from our internal WSUS to Microsoft’s web-based one, changing this back to internal resolved this error. Must be something to do with our web proxy.