The IDM AD driver requires a filter DLL to be installed on all DCs for password synchronization. Unfortunately, it seems as if the IDM setup does not always update a previously installed version of pwfilter.dll (and associated files) properly.
This INF installer can be used to update those files so they will be used after the next reboot:
place setup_pwfilter.inf in the C:\Novell\IDM_PassSync folder on the machine where you installed the IDM AD driver
right-click on setup_pwfilter.inf and choose "Install"
verify file versions of pwfilter.dll and psevent.dll in your system32 folder
Many thanks to Alex McHugh for adding x64 support and fixing some bugs!