Currently it looks like the lice SDK returns error 500 for all request. Also the interactive SDK Microsoft provides here returns the same error:
http://isdk.dev.live.com/dev/isdk/ISDK.aspx?category=scenarioGroup_core_concepts&index=1
My application work without any changes for over 24 months. Has someone any more details or a workaround?
Update: I tried the following API calls both with the same result:
Finally, and after a very long downtime (more than 20 hours) the Live API is up & running again. Unfortunately, there is not even an official announcement from Microsoft.