Supercomputing power is a solution to the users need for more accurate results and larger problem sizes. In addition to the problems that arise in the design stage of a parallel program it is difficult to localize and correct errors in the testing and debugging phase. Where memory hot spots and bus contention are problems with shared memory architectures, nondeterminism arising from message races and the lack of a global clock are severe problems using distributed memory machines. Due to errors which are introduced through communication, the debugging process has to be extended. In this paper we discuss an approach to error detection of concurrent events in distributed memory machines. With our event graph manipulation tool ATEMPT the user can investigate a global communication graph in order to find errors in the communication structure. Also investigations can be made to find message races in a certain program run.