Hello,

if you experiment issue when saving positions associations try to check the chmod permissions for the file used to store data. The error is related to a file write error.
the file used is this:

joomlapth/templates/responsivizer/framework/modules/dbpositions.json

As a side note if you need to assign existing modules to a responsivizer position, you can also use the Modules Manager and the 'Make mobile' button to migrate modules from desktop to mobile template.

Best regards

John Dagelmore