Application Sharing - Not in Call

[Rob]

Whenever I try to use application sharing, everything looks like it's
working, but when trying to select the application from the application
sharing window, everything is gray and the header says Not in Call.

I've been able to use remote assistance between the machines, but not
application sharing. Both machines are behind a Linksys wireless router
with UPnP enabled.

Any assistance would be appreciated.
-Rob S.