TBXLLUDFNumberName UDF throws "Runtime Error 13: Type Mismatch" when Selected from Insert Function dialog

[GCuser99]

If I click "fx" (Insert Function) on the formula bar and then select TBXLLUDFNumberName UDF, I get two "Runtime Error 13: Type Mismatch" errors back-to-back before Excel presents the Function Arguments dialog. If I then enter a number argument it works fine.

On the worksheet, if I select the cell containing the function, and enter a string argument like "5" or "", I get a "Runtime Error 13: Type Mismatch".

I'm thinking those two behaviors might be related?

BTW, this behavior does not happen with the other function TBXLLUDFRomanNumeral.

I'm using Excel 365 64-bit.