If you are not familiar with break-points find some ABAPer who can help you. Because purpose of the break-point is to debug why program throws that error. You can't do this if you don't know how to set a break-point.
If you open that Method you can see a comment about LUW. Hope debugging can tell what is wrong with it.
Programs usually don't stop working for no reasons. What has changed in this system from the time this was working?