Luckily, I found the older version that works is still available in the plugin section of the forum.

This one still works fine and works with 1.5.6a.
EasyPopulate V4 - Version: 4.0.36.ZC

The version on GIT HUB Easy Populate 4.0.37.6 - 02-08-2017 does not work and has the import error.
If you have time maybe you can look into this issue and find what is the problem.

In the meantime the solution for anyone with the same problem is to use the version listed above.