I have had that sort of issue occasionally caused by a non-printable
character which has somehow got inserted into the source, try
re-typing the line where the parameter is passed and where it used to
eliminate that possibility.
If not that does it help if you call it with a string, blockedcallsign: "text"
Also try using the variable in the partial just as a string rather
than inside the button_to function, to prove it is not to do with the
context where you are using it.
As a final test try changing the parameter name. Not sure why it
should help but if nothing else it might give you a clue
Colin