Enabling support ticket comment as entity reference triggers PDO exception

I am trying to specify a support ticket comment as a canned reply. The idea is that a support engineer can select a previous support ticket comment as a canned reply and update a ticket.

So, I installed the entity reference module, added a field to the support ticket content type called Canned Reply, selected Entity Reference as the field type and select list as the widget. In the widget configuration page, I selected Target type as 'comment' and target bundle as support ticket, with the mode being set to 'Simple (with optional filter by bundle)'.

When I save these settings, I get the attached PDO error. Not sure how to fix this. Drupal version is 7.16 and all the relevant modules are their respective latest versions.