Importing clips from other UMotion project fails because of constraint setup

I'm trying to import some clips from UMotion project to another, but it's failing because I'm getting the error "The constraints of 'IK_Foot_L' are not compatible with this project. The constraint setup needs to be exactly the same."

Is there a way to get more specific info about this? The 2 projects were generated from identical rigs, and they both used the IK Setup Wizard, so I just wish I had more clues to figure out what is going wrong.

Thanks for your help! :)