Your Oscall value is already programmed in the OTP. Pic Start tries to
program the Oscall vallue it's got in it's own memory into the 12Cxxx
but finds that the PIC's memory is not empty. It will not program it
then and gives you an error message.
As this only happens after your main program has been stored in the PIC,
it is OK to just ignore it.

BTW, I use Picstart Plus via MPlab 4. I get a message that the
callibration has already been programmed on a OTP.

Hope this helps.
Quentin