Lock Scheduler 3.6 with ACP 7.1 during installation AND AT RUNTIME.
Testing under all of the combinations was time consuming. I discovered the problem of the HotFix level this way though.
The locking needs to be such that newer versions of ACP being installed will catch people having old Scheduler installers (and giving a reasonable error). It also needs to be resilient to any ACP hotfix (the third decimal number).