Crystal Reports 2013 - Code 39 Barcode

Hello,

I'm getting an error when I try to convert a field to a barcode using CR 2013. I'm using the code provided by:

http://www.azalea.com/crystal-reports-custom-functions/code-39/

But when I try to run and view the report through the Crystal Report Windows Form Viewer, I get the error attached in the image.

I do not get this error when previewing the report in CR 2013 itself.

Any suggestions?

Thanks,