How do I resolve Assertion error matheditio:1508 in Mathematica 4.0?

When executing notebooks in Mathematica 4.0, you may get the following error.

Mathematica has detected a possible internal error. If possible, report the error to support@wolfram.com, quoting "Assertion 'nboxesToSend == 1' failed at matheditio.c:1508", and describe in as much detail as possible what you were doing when the error occurred. 

Please contact Technical Support directly with your license number (found by evaluating $LicenseID) to receive a fix.

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Questions or comments? Send email to support@wolfram.com.