Texas Instruments TI-83 Plus Manual Book page 49

Error in Xmit
This problem is usually associated with the unit-to-unit cable and
its connection between the TI 83 Plus calculators. Make sure the
cable is firmly inserted in the I/O port of each calculator.
If you continue to get this error, please contact TI Cares™
Customer Support.
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 Customer Support.
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
Customer Support.
TI-83 Plus Polynomial Root Finder / Simultaneous Equation Solver Application Page 49