Cubase 5, some VST's configuration error message


I can’t get, for instance, VST Ixox_Flute to work in Cubase (and it happens with a few other plugins/dlls as well). Please if someone could know how to fix this error message, I would be very appreciated ::

“This mixer configuration expected “Ixox_flute” to have Output 1: Stereo.
The instrument currently has Output 1: Mono, Output 2: Mono,
The instrument will be silent.”

Yet, when I load it into Reaper, for instance, no error message pops up and the plugin works quite fine.

Any idea how to fix this? Thanks much for any response! – .artemis