In line 35 of "handler.php" file specified in error message posted in the first post of this thread, indicates that the plugin thinks that we're wanting it to copy the existing record while not leaving the name field blank...
Going on that information, I can now able to reliably re-create the error on my system as well. I can now re-create it every time by, in the "Copy Subscriber Role" box on the right-hand-side, typing a name *exactly matching the name of an already-existing role* into the "Name of copied role" textbox and clicking my mouse on the "Copy" button.
Corresponding to the time when you saw the error message in the log, can you confirm again which button you clicked? (maybe even run through the motions again and tehn check in the log again, to have a fresh case?)(i mean was it definitely the Create button and not the Copy button?) (and not the enter key which might have represented a different button click like the Save button?)