When I click on the URL in an Outlook Calendar invite for a Lync meeting from my Lumia 900 (Windows Phone 7.8), I stopped getting the usual callback from Lync to join the meeting. Instead, I end up in IE with the message "We're having trouble getting you into the meeting. It's possible you're using a bad URL. Try calling into the meeting using the phone number on the invite, or ask the organizer to drag you into the meeting from the Contacts list." Note that I have already uninstalled Lync, shut down phone, the restarted and reinstalled Lync - behavior is the same.
Diagnostic message is in a text box, but I can't copy it - typing it here (obfuscating URL, but it works on my PC):
Machine: 000DC02L50FE1ABrowserID:Mozilla/5.0(compatible; MISE 9.0; Windows Phone OS 7.5; Trident/5.0; IEMobile/9.0; NOKIA; Lumia 900) Join attempted at (UTC)8/8/2013 6:37:16PMTelemetryId:7905e864-4e37-466d-ab98-912aeb3cf865IncomingURL:https://join.xxxxxxxxxxxxx)\>Error: Meeting URL format may be invalid