During a migration from OCS R2 to Lync I started having a problem when testing UM access to voicemail; displayed an error on call or redirect and disconnected. Ran some tracing and the following error was flagged in the diagnostics field:
MS-client-diagnostics: 52059;reason=”Invalid SDP in response”
Turns out this is caused by the VoIP Security setting in the Exchange UM Dial Plan option. Whilst I used to have this configured as ‘SIP Secured’ when operating with OCS R2, it would appear it now requires to be ‘Secured’ to function correctly with Lync2010.
So, to fix: Exchange > UM Dial Plans > Properties of your Dial plan > VoIP Security = Secured
Hope this helps