This is driving me crazy!

I developed a very simple webservice, just one webmethod that returns a datatable.

Then, in my ASP.NET 2.0 website, I added a web reference to this webservice, and used the ObjectDataSource to databind the results to a DataList. 
So far so good, everything works like a charm on my dev machine.

BUT when I put this website online, it doesn't work anymore!!!

When using Eval("FileName") in the DataList I get the following error:

System.Web.HttpException: DataBinding: 'Webmedia.GetImagesResponseGetImagesResult' does not contain a property with the name 'FileName'.

Webmedia is just the name I gave to the web reference, and GetImages is the name of the Webmethod that I call in the Webservice.
FileName is one of the fields in the DataTable that the webservice function returns.

When using Container.DataItem("FileName") the error changes to:

System.MissingMemberException: No default member found for type 'GetImagesResponseGetImagesResult'.

Again, no matter which technique I use, it works perfectly when I run the website on my local Windows 2003 server.
(it doesn't matter whether I run the webservice online or locally as well, it works both ways)
Only when I run the website from the server on the Internet, I get the above server errors!
I even tried on 2 different hosting servers to be sure it isn't related to the webserver itself...

Anyone please have a clue what is happening here?