When loading or updating a large Excel spreadsheet (1.5MB) I occasionally get this error.

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Microsoft Excel - <filename>: excel.exe - Application Error

The instruction at "<hex address>" referenced memory at "0x000000000". The memory could not be "read".

Click on OK to terminate the application
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This is happening on 2 different machines both running Windows NT4, one with SP5 and one with SP6 installed.

(I have also got the same error installing some Oracle software off a CD on to a 3rd PC).