I have a hybrid environment with an existing 2003 server and a 2010 sp3 hybrid server. Everything has been working perfectly until this morning I am getting reports that users with 2003 mailboxes cannot access online free/busy information. I have confirmed:
2003 --> 2010 works
2003 --> Online doesn't work
2010 --> 2003 works
2010 --> Online works
Online --> 2003 works
Online --> 2010 works
As far as I know this has worked in the past, any ideas what could be causing it? I have looked at the permissions on the PF on 2003 and the default is set to Editor as required. I am not sure what else to look at since everything else works.