I'll give my captain obvious answer, don't know lyncs config details well I'm not really a sysadmin.
503
You've got the request or lyncs response blocked on ucwa or something else in between. There's somewhere to configure that policy it's talking about.
try fiddling with this request to get your policy list (I guess there's a shot that's blocked too) https://msdn.microsoft.com/en-us/library/office/dn323680.aspx
403 is forbidden.
I don't think lync has port 80 http open by default.
Gotta drop some configuration on your tmg/isa server it looks like to open that stuff. The policies are probably in there somewhere too.
https://technet.microsoft.com/en-us/library/hh690011(v=ocs.15).aspx that has a snippet for how to open port 80 at the end, and I'm going to take a wild guess at what your trying to do and say the first part is likely relevant too.