Cannot load .pit file with Quest vWorkspace Client 7.6 from External (Remote Access through Juniper SA https)

We are getting the following error message if we want to start VDI Session via Remote Access (Juniper SA-4500)

The Connection to the Remote Access (Juniper SA-4500) works fine an we are getting also the portal with the link to our internal Quest Web Access site. When I log on to the Quest Web Access with my credentials I'm getting the following error message

Quest vWorspace Client

Cannot load file "C:\Users\xxxxx\AppData\Local\Microsoft\Temporary Internet Files\Content.IE5\xxxxxx\xxxxxxxxxx.pit

From the Internal Network everything works fine. I can connect via Internal URL to the WebAccess Site, use my credentials and log on to my VDI Desktops

We are working without the Secure Gateway. The internal and the exernal URL are different.

The internal URL and the external URL are different like

Internal : http://lt-portal. .local

External : https://portal. .ch

Technical Data :

We are using Version 7.6.305.791

Web Access Connector 7.6.0.791

Client OS Windows 7 Enterprise  with SP1

IE 9.0.8112.16421

It's difficult to troubleshoot because there seems to be no entries in the eventlogs of client, webaccess server and connection broker

I would appreciate any help.

Regards Thomas