To use load balancing and Sitefinity you need to setup the server environment as described in this
part of the documentation. Also as Jean already mentioned you will need load balancing module for Sitefinity that will manage the communication between the servers. The load balancing module is a payed add-on with Standard edition and comes out of the box with Professional, here
you can review the official information.
Also when you have setup the whole environment you will need to put the machine keys of bot servers (if they are two) in Sitefinity web.config. Is your load balancing environment already setup this way?
the Telerik team
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