Issues with Portal-Access via Webtop when using DNS name

Hi All,

 

I'm having some issues getting a Portal-Access link to work.

 

I'm using APM, have a webtop working, but when I click any portal-access links that I've set up that direct to internal resources, I receive a 400 Bad Request. This is if I browse to the APM using its externally resolvable DNS name.

 

If I browse to the webtop via its public Ip address and do the same, the portal-access links work!

 

Hopefully this is a simple one, any ideas?