Add a new field to existing data base interface

I've inherited an existing .rpt file and need to make enhancements. Using .Net with C# my application makes an instance of a ReportDocument and then for each subreport uses the SetDataSource method to pass a DataTable.I need to add a new field to the data base interface. Unlike adding a new parameter which is as simple as right clicking and selecting new, there doesn't appear to be something similar for the data base interface. Given my interface I really don't have a "data base" existing in the traditional sense, or one that can be connected to and browsed. If I use Database Expert, with one of the existing data base interfaces it shows its properties as Type Acess/Excel (DAO) with a database name of a path starting with c:\Inetpub\.... This path seems to imply an IIS installation but I have no such path on my PC and everything is working fine. This seems odd? I was unable to find any way to simply add a new field.

After a lot of searching I used the Field Definition Only to create a .ttx file containing the existing fields plus the new ones. I then changed the data source for the existing data base to use this. All this seemed to work just fine until we tried to test our application on other than my PC. On another PC the application dies with "Failed to load database information". I though it might be related to these .ttx files but hiding them on my PC still enabled the application to run on my PC. If I copy the entire contents of my bin directory to another PC the application fails so there must be some new driver the was installed on my PC.

Remember, the basic problem is: how to add a new field to the original data base interface?

Any advice would be most appreciated.