Hi,
We've been using LCS 2005 SP1 for a number of years now, and I just found out you can use the IM and presence through ISA server without the need for a SIP filter (I know we can't use video/voice & sending files without one). So I've tried to setup LCS through ISA following this guide: http://technet.microsoft.com/en-us/library/cc713340.aspx (I know its for LCS 2003 but I assumed it would be similar for 2005).

I've been testing externally using a 3G broadband card, or on my home wi-fi, and I've found that Communicator won't sign in, and I get an error saying 'Cannot sign in, possibly because the authentication server is unavailable to verify your sign-in information'. However I have found that if I connect to our network, either by VPN or plugging in a LAN cable when in the office, then sign-in, sign-out, disconnect from the network, and connect externally again, then try signing in, it connects and works ok. But if I logout of WIndows and back in, I get the original error.

Can anyone suggest a reason behind this behaviour, or a solution to be able to sign in without requiring connecting to our network first?

Thanks

Ben