No Schema type for mysql type datetime error while creating view to show webform submissions
You likely already resolved this, but I just ran into the same issue.  Here's how I resolved it:

I applied the patches to the Schema module listed here: http://drupal.org/node/1237974.  

This got rid of the error, but because i had a db_prefix on my tables, I could not adopt them.  In order to get that working, I tried the patches here (http://drupal.org/node/894074#comment-6459584).  It didn't work for my view, so I logged in via PHPMYAdmin and removed the prefix dr_ from the webform view (instead of dr_webform_myviewname, it's now webform_myviewname).  This allowed me to adopt it.  

I'm not saying it was pretty, but it is working now.  

KMT