I recently upgraded to the Feb 23rd release on my collie with OZ 3.3.6, from whatever was there before the 23rd. Opiemail stopped working for me and I get the same error. 0.4 worked just fine, but 0.5 seems not to. (All the dependencies have been upgraded too) Im either missing something or some packages in the latest feed have some problems, as should be expected, being an unstable feed; but from what I can tell, more than just opie-mail has been affected.
~AIG