For Receiver 3.4, Citrix in their infinite wisdom have taken away the abilty to change the PNAgent URL Value location with a registry string value and have now stored it as a binary key inside HKCUSoftwareCitrixPNAgent “Configuration Model 000″.
You can use a script to read and edit it,
http://www.remkoweijnen.nl/blog/2012/02/13/scripting-citrix-online-plugin-settings
or the citrix tool to just read it.
http://support.citrix.com/article/CTX118255
The easiest way is to set it up on a clean machine and just export the key. The easier way would have been for Citrix not to make your old GPOs that edited the registry useless.