Sometimes, an SAP process will stop working with an error message, or an abend. Unlike with a dump, it can be difficult to find exactly where the problem occured. What you should do, is get the technical name and number of the message - e.g. RS 100. Set a breakpoint at the start of the process (or run the process with the debugger switched on). As soon as the debugger is in some abap code, set a watchpoint for sy-msgno. In this example, you should set a watch point for sy-msgno = 100. Then hit F8.
The process will continue to run until sy-msgno has the value 100.
Check that the message ID is correct, according to the message - RS in this example. If it is, then you are at the place where the error occurs. You can usually back trace a few steps to find out precisely what was causing that error to be triggered.