While trying to deploy data, we are getting a successful meta-data deployment.
However, during the data deployment phase we are erroring with the generic sql connection is already open. 

Within our code prior we are able to open and close the sql connection fine, but once it gets to the data deployment phase in the DBEngine it fails.  We have a couple of machines this works fine on, but there are a couple that just won't work.

Any thoughts as to what might be causing this? 

I assume that you are deplying manually using th DatabaseMigrator class...this is the only time that I have seen this before.  But in this case, it is really simple to fix.  Just dispose of the DatabaseMigrator class and re-create it between the meta-data deployment and the data deployment and it will resolve the issue.