Hello, first, you need to reference your Tool in a given set as :
<PlugIn Id="_NewTool" Type="Box" DimX="0.5" DimY="0.1" DimZ="0.1" ID="B1" FrameID="F1" Set="B1_Set"/>
After that, you should replace your collision detection "Body/discreteElement" by this one :
<PlugIn Id="_ManageCollision" Between="Body/Body"
BroadPhase="Raw" Set1="B1_set" Set2="Global"
NarrowPhase="WithShape"
CallBack="Standard" Stiffness="1e7" RestitutionCoeff="0.1" />
It should work !