It's a little surprising to hear, since WM6 is so close to WM5 in its underpinnings, but the SlingPlayer for Windows Mobile isn't working on WM6 yet. Never fear, though, the folks at Sling are working on it and they'd like your help -- in the form of a private beta for the update. Sling's built up a lot of street cred with the mobile crowd (or with me, anyway), so I suspect that it won't be long before this private beta becomes a public one.

We are actively working on a new version of the SlingPlayer Mobile that will add support for Windows Mobile 6 and are currently looking for people to participate in a private beta of the new Windows Mobile 6 compatible version of the SlingPlayer

Read: Sling Media - SlingPlayer Mobile is not currently compatible with WM6