Thanks for the report, I will double check to see if I can reproduce this issue locally (it will probably be not before Monday). I might have more chance of success if you tell me, 1) your model 2) the process that you are using 3) which re-weighing you try to perform 4) which operating system you are using (and if not standard which version of python, numpy and gcc you are using) Now the issue is related to the reweighting functionality. That part of the code use a special method to evaluate the matrix-element since it use a python binding of a fortran code. (The reason is that such code is IO/parsing intensive and this is a nightmare to do in fortran but that the matrix-element needs to be in fortran for speed reason) Looks like that such link fails to be created in your case. Cheers, Olivier > On 2 May 2018, at 15:31, ComplicatedPhenomenon