The invention is directed to a computer system comprising a server and a client and a method for operating a remote procedure call handler in the client and the server. The Method for operating a remote procedure call handler in the client according to the invention comprises the following steps: a) sending a collected call message comprising a number of call messages to the server, b) receiving an error message indicating a successful or erroneous transmission of the call messages comprised by the collected call message, wherein the error message indicates an erroneous transmission of at least one call message, wherein said at least one erroneous transmitted call message is retransmitted by the step of c) sending a further collected call message comprising said erroneous transmitted call message as well as a plurality of further call messages.