Reinaldo,
You've run into a common situation with Paradox reports. Namely, reports cannot contain (or refer to) code stored on a form. Each Paradox document (form, report, script, etc) has a local scope, which is a programming way of saying that code is only visible on the document it appears in. Put another way, your error message is telling you that the report has no idea that getCurrencyAsText() exists on your form.
As a result, you'll need to store the actual result of getCurrencyAsText() in your table in order to print it with a report. There are more elegant ways of handling this, but this is the easiest to implement for some people.
Depending on your experience with ObjectPAL, I'd suggest adding a field to your table that's large enough to hold the results you're getting and then reworking your existing code to update that field with the results of getCurrencyAsText().
Without knowing your Paradox version or current implementation, I can't be more specific; however, we can help if you post some code.
Hope this helps...
-- Lance