What errors are not being trapped?

>I've set up a VFP8 application with a global ERROR handler in the typical format of ON ERROR DO ErrHand WITH ERROR(), MESSAGE(), LINENO(1), PROGRAM(), SYS(2018).
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>Has anyone encountered a situation (such as a VFP Bug) when the Error Handler will not catch errors and the default VFP error dialog appears?
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>Please note, I have no overriding error handling code in any Object or TRY..END TRY methods. Also there are no syntax errors in the Error Handler itself.
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>Is it possible to have an Error without the above parameters?