Error message when invoke flow

Need some help. Running a workflow with 3 call outs using attended robot, to explain what do do in application. Running fine when I test it alone, but as soon as I put it in an invoke I got error message. Following error:

Invoke (Name of flow) workflow: The invocation of the constructor on type ‘UiPath.Callout.Activity.CallOutActivity’ that matches the specified binding constraints threw an exception.

Anyone knows moore about this and could explain what to do to fix it? Could not find any answer elsewhere.