Here's the fix.
I had the same problem you're having Marcel. I tried to rename the Windows Media folder, I tried to delete cookies in IE, I tried all the Sirius FAQ's, I spent hours on the phone with Sirius tech support, I went to every forum.
I am running Windows Vista Business, IE7, WMP 11, Latest version of Adobe Flash.
With "Enabled Protected Mode" selected Sirius not play within IE. You must remove this security setting. I've found the best way to do this is to add Sirius to your trusted sites. This way other non-trusted general web sites will be subjected to the Microsoft recommended Protected Mode.
Here's how I fixed the problem:
1. Navigate to the Sirius player website (http://www.sirius.com/sirius/servlet...layer?stream=&).
3. Click a station.
4. Your player will say Ready.
5. Go to the IE Tools Menu.
6. Choose Internet Options.
7. Click the Security tab.
8. Click the Trusted Sites icon.
9. Click the Sites button.
10. Uncheck the "require server verification (https://)” checkbox at the bottom of the dialogue.
11. Add http://www.sirius.com (this should auto fill) to your trusted sites.
12. Click Close.
13. With the Trusted Sites icon still highlighted uncheck the "Enabled Protected Mode" checkbox under the Security Level setting area. My Trusted Site security is set to “Medium.” This is default.
14. Click Apply.
15. Click OK.
16. Restart IE.
You should be good to go.