Streaming Player does not send Request to DRM Server

Hello,

we are currently testing our PlayReady DRM server with roku box .
We experience a strange behaviour: while all relevant links from offical Microsoft Testpage work fine, our own Server (which works fine everywhere else) does not receive a request from the Player:

Excerpt from protection header (Base64 encoded):

[1][1]16AESCTR
[…]
<LA_URL>SERVER_URL/CSM/RightsManager</LA_URL>
<LUI_URL>http://SERVER_URL/CSM/RightsManager</LUI_URL>
[…]

But no call is made…

As I said, with official MS links it works fine. We traced, and we see, that no call to the license Server is made