Custom service is giving errors

This is kind of a weird one. Basically I have an application that runs reports. In the process of creating the report, it takes a number and converts it to a 3 of 9 barcode. This works fine when I run the application manually. However, when I try to run the application using a service that has been created, it doesn’t convert the barcode. It just gives me the number in between two asterisks. Any ideas?