If a job of type "External script" (CL_EXT) contains a node variable in the path that refers to its external script, the job fails with error in the History Trace:
CL non executable by this user or not found
An additional symptom is that U_ANTE_UPROC is not executed.
So this occurs, for instance, with the following node variable:
... and inside the CL_EXT the following path to the external script: