运行失败提示，请问是什么原因

Unhandled exception in script

Failed to execute script 'subjects match'due to unhandled
exception:'Worksheet sheet1 does not exist.'
Traceback (most recent call last):
File "subjects_match.py",line 200,in <module>
File "openpyxl\workbook workbook.py",line 287,in_getite
KeyError:'Worksheet sheet1 does not exist.'