Module Broken After 5.4 to 6.1 Upgrade

I recently updated our site from 5.4 to 6.1 which broke a custom module that I created. When I try and access the module data or create a new module item, I get the following error:

An item with the same key has already been added.

I followed the upgrade instructions and everything else seems to be working great. Since there is already content loaded into this module, I don't really want to have to delete and re-create. Has anyone else run across this issue after upgrading their SF version?

Thanks,
Greg