In this post we will how to resolve error "The operation could not be completed" infopath 2010 error. Also you can check out my previous posts on:
This error comes ususally while creating the data connection.
This error can be solved by creating a top level site collection. Infopath data connection always follows top level site collection. Otherwise it will not work.
So make the site as top level site collection and try creating the connection. The error will not come.