Joseph Wisniewski , Jun 01, 2011; 01:57 p.m.
It's not a "3rd party conflict". The Metz, in "manual servo" mode doesn't do CLS.
The D90 makes several flashes, a message to the remote flashes to do a metering sequence (which is a bunch of tiny flashes really close together) and another message to set power on the remotes, then finally, a plain old "flash" flash to trigger the remotes.
Apparently, at 1/128 power, the Metz has enough power and speed to trigger from the messages and then trigger again on the main pulse. But when you turn the power up, it exhausts itself on the messages, and doesn't have anything left to take the picture with.
Take the D90 off commander mode, don't use M ---, just use the plain old manual flash mode, turned down to 1/128 power, and you'll be fine.