Excel 97 SR2 often crash in sudden

Hi all,

When I'm working with excel file, It often shows an error msg
with title "excel.exe - Application Error" suddenly and the msg is about
"The instruction at "0x3070ab13" referenced memory at "0x000000000". The
memory could not be read". After closing it and restart the excel again, it
seems going back to normal again. Anyone know how to solve it ?

Ellis