I was running into this same issue today and this thread came up - but had an incomplete answer.  Since I had to dig further to find the answer I figured I should update this to give a complete answer so others (if they come) can get the solution they need.

Can you find it in your heart to forgive me? My intentions were only meant to be polite by appending a solution to this thread - as I stated: I came across this thread today because I had the same issue - but there was no immediate solution to be found.  I found plenty of wrong/incomplete info on this site. That is why I left the final solution to help other user who are not in the know. 

Even this blog post by Will Strohl is wrong - it's only if you read the comments that you get your answer: that there should be no .ascx on the skin path

I even somehow got this busted wiki page that doesn't go into details - here's another post that doesn't go into detail. And many more forum posts that touch on the subject with no deep info. So once I found the solution - I placed it at one of the first results I had pop-up on my search - in case other/future users need it.