I think I can help!
Originally the software for the Kestrel 4000 series was not compatible with the 4250. Oops ... 
It has long since been updated and the most current version is available on our website. You can always download the most current version there.
Go all the way to the bottom of the page. We have Vista drivers now as well.
Now if your having problems with the actual physical cradle ... I'd have to look into that. I haven't heard it before.
Let me know if that answers the question or if I should do some more digging.
Thanks!