6.7.1 Using Old WFT - getting error

System

This is probably something simple,. but I've copied one of my old WFT files over to our 6.7.1 server, updated available_templates.cfg with the identical section from the old setup for that WFT, made sure all the necessary extra files, UNIX groups, etc. are in place. I kick off the workflow, it appears in the pop-up as a WF to select. I select it, then BAM:

TeamSite: Wrapper
Error: Invalid session string
# very long string of characters # received

WTF? What did I miss? I've never seen this before.