I´m not very happy about running helper-processes under admin-credentials like suggested here, specially when they should run in a batch-job.
So i stepped into the deep ... and found out, that WRAP, even if it does not tell you anything about any error on the commandline,
it writes into following logfiles C:\Users\<user>\Oracle\ORADIAG_<user>\DIAG\CLIENTS\USER_<user>\HOST_4145470312_76\ALERT\LOG.XML
(not sure, if that number after HOST_ varies on different installations)
Having a look in these logs, i´ll found out, that during that clumsy oracle-installation process, it simply has forgotten to create
the directory %ORACLE_HOME%\log\clients which obviously is required for the wrap-tool and also needs read/write-access.
After created that folder and granted read/write to it, wrap works fine ...