Hi,

>The arguement passed to this program is simply a string with a length of between 10 and 26 characters. Some examples might be:
>
>000002W12S456
>000817BAKER10127
>
>The first six digits represent a client code and the follwoing digits, from 4 to 20, represent a case number.
>
>No start code is passed with the string.

Since it contains alphanumeric content it will be CODE-B - but to work with the code you quoted you should prepend the CHR(104) to the string before passing it to the procedure. This should then calculate the checksum correctly. I can only assume that the additional prefix and suffix characters are font specific and used to flag that the enclosed content is a barcode. Whether these are correct for the font you are using I've not idea - check the docmentation for this.
HTH,
Viv