Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 1060 6GB/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 419.35
Broken: version: 2.80 (sub 51), branch: blender2.7, commit date: 2019-03-24 00:06, hash: rB79f67acccb36
Short description of error
The buttons to transfer animation from one to the other dont work, also they are named incorrectly the one to transfer from IK to FK is named FK2IK and vice versa
Exact steps for others to reproduce the error
Open up a rigify rig, do some animation on the IK hand, push FK2IK or IK2FK and you'll get an error like the ones here
I can privately send a file for testing upon request.