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"
Reboot
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!
You can use the following command to run this from the command line (for example on a Windows Server Core box - where you can't right click and select install).