This error is pretty uncommon and we don't encounter many users who actually see it.
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While this error pops up in the PDF2XL program, it is specifically related to Excel. 

You shouldn't see this error at all if you are using version 7.0 or higher as Excel is not required for a conversion, however, if you are using an earlier version, there are a couple of things you can try.

While neither option is considered an ideal solution, regrettably, this is not something we are able to correct, which is one of the reasons why version 7.0 features the conversion without Excel requirement.