ASP.NET AJAX configuration in Sharepoint Farm using multiple Web Front-Ends

Hello,

We have a ASP.NET Application using in this case Telerik Ajax components.
Everything works fine in our own SharePoint Farm with one Web Front-End but
when testing same Application in user's environment where a Farm has
multiple Web Front-Ends problems arises.

For example Ajax stops working suddently. E.g. Ajax based actions in Grids
works only once and launching and closing a Ajax based Popup Window seems
to stop Ajax working.

Does anyone know what has to be configure differently when Ajax based
Application is running with multiple Web Front-Ends?
What could cause this kind of behavior?

Cheers,

Michael