The Runpath should give the name of the folders where the ECLIPSE simulations are to be executed. It should contain at least one %d-specifier, which will be replaced by the realization number when ERT creates the folders.
Optionally, the Runpath can contain two more %d specifers, which will be replaced by the first and last report step of the simulation. By default, Runpath is set to "simulations/realization%d".
When running with LSF it is essential that the Runpath points to a network disk which is accessible with the same path from all the nodes in the cluster.