Why there are error messages appearing in the display?

There are many potential issues with error messaging. Problems such as data type, domain, memory etc. are all internal and misuse issues and not issues of a broken device. If there are no problems with the user input and there are still error messages then it is most likely an issue with the keyboard or the motherboard malfunctioning. This problem would most likely be solved by the replacement of the TI-80 motherboard.