KB000435: What does Error Message "Unable to start MSTOP! Fix top.mac…" Indicate? - MS ChemStation 

This usually means the default sequence has been deleted. A valid sequence file named HPCHEM\1\SEQUENCE\DEFAULT.S is necessary to start a session on instrument 1. If this file is missing, copy HPCHEM\MSSETUP\SEQUENCE\DEFAULT.S to the above directory and try to start the ChemStation again. If this does not clear the problem, it may be necessary to reconfigure the instrument. To reconfigure: select Start...Programs...Productivity Tools... Config. In the Config panel, select Instrument...Instrument 1. If the information matches your instrument, click OK. Then select Files...Save configuration. It is not necessary to change any values in the configuration panel unless you know they don't match your instrument.