If you have followed the directions to cash out (found here) and the money has been returned to your account, make sure you have entered your email address correctly. I know, it sounds so obvious but, for hours, I was having trouble logging in to one of my accounts. I checked my email address and it was correct... well, the part before the @ was, but I wrote gmial.com (yes, this tiny little mistake had me so frustrated and it took me almost three hours to figure out). So, double check every part of your email address (even the obvious parts).
Even though you've been using PayPal/Dwolla for years, it doesn't mean your account is set up to receive funds! Yes, you can successfully pay for things without ever having to set up your account to receive funds! I had NO idea there was a difference either!
Make sure you login under your country... here are the links to login by country: Australia, Canada, Denmark, Norway, Sweden, United Kingdom.
If you've followed the cash out directions, checked your email address, and set up your account to receive funds and your funds are still being returned, email support... they are the only ones who will be able to tell you what the problem is.