Thanks for posting in answers.slingbox.com! I'm sorry to hear you are having trouble connecting to your Slingbox via WD TV. We do not have an ETA, but there will be a firmware update to the Slingbox 350 that resolves the issue.
For now, I would check out this links and try this, as it may be a work around:
I want to apologize for any inconvenience this has caused you.
The Sling Moderation Team