I probably didn't do a very good job of explaining the problem I was having.
In any case, I was able to resolve it by doing two things:
1. I reviewed all of my data connections in InfoPath until I found the one that was returning two fields with the same name of 'siteid.' I had included a table's primary key, siteid, in my SQL select statement. However, it appears that InfoPath likes to include primary keys in select statements automatically, which is what caused the error. I removed the 'siteid' field from the SQL select statement that I had manually included and just used InfoPath's automatic primary key.
2. I followed S.Y.M. Wong-A-Ton's recipe #85 from Cookbook #3 for using the Execute() method of the WebServiceConnection class. This book is the most useful resource I have found on developing InfoPath forms anywhere--online or in print.
Thanks,
db