Texas Instruments TI-83 Plus User Manual page 57

Invalid Signature or Certificate
Either this calculator does not have a certificate to run the
application, or electrical interference caused a link to fail. Try to
install the application again. If you continue to receive this error,
contact TI Cares.
Other Errors
See pages B-6 through B-10 in the TI 83 Plus manual for
information about the specific error or contact TI Cares.
TI-83 Plus Conic Graphing Page 57