We upgraded ALM from version 17.0.1 to version 25.1 and now we can't start tests from Jenkins anymore.
Failure message in Jenkins: 

Starting test set execution
Test set name: RegressieTestSirius, Test set id: 306
Class not registered

Class not registered

Error: Could not create scheduler, please verify ALM client installation on run machine by downloading and in installing the add-in form:
https://mfalmtest:8443/qcbin/TDConnectivity_index.html

URL is only internal reachable !!

But on this specific machine we can start ALM and run this test from the ALM Client without any problem.
Build step 'Execute OpenText functional tests from OpenText ALM' changed build result to FAILURE