External Lync clients can't join meetings - get kicked out with "You have left the call"

[RomualPiecyk]

My users connecting remotely (ie. from home) from their Lync clients installed on their PC are unable to join any meetings. It tries to connect, but then gives the status "You have left the call."

Internally (ie. in the office) it works fine. Additionally, the Lync Web App clients also works fine, internally and externally.

Some details on my enviroment:

Edge - Lync 2013

Front End Pools - one 2010 Enterprise (albeit one server), one 2013 Enterprise (two servers)

A standalone Lync 2010 A/V server exists as well.

Meet and dialup records internally point to 2010 pool. Externally, they point to 2013 access edge.

SRV records on external DNS are _sip._tls 443 and _sipfederationtls._tcp 5061, both point to access edge.

SRV records on internal DNS are _sipinternaltls._tcp 5061 to sip (which is an "A" record with IP for 2013 FE pool), and _sip._tls 5061 to access (which is an "A" record with the internal IP of the edge server).

Any thoughts on how to troubleshoot this would be most appreciated. Thanks.

Ron Piecyk
romualpiecyk@gmail.com