We have a number of machines on our local lan (no firewalls) with Office Communicator 2007 R2 (with Enterprise CALS) installed on. All but a couple of them can share their desktops with no problem at all. However on these few machines when sharing desktops the remote party can only see a black screen with a pause symbol (2 thick white lines, like the old VCRs used to show).
These machines can see other peoples desktops when they are invited to view them.
Does anybody have any ideas what is the issue? I have tried reinstalling Communicator on these machines.