Hi Vewia,
What version of the Omnipressor plug-in are you using? You should be able to tell by instantiating the plug-in and mousing over word Eventide in the plug-in GUI. When you do, the version number should pop up. If you are not yet using 2.1.3, please download and install it from here: http://eventide.com/AudioDivision/Support/Plug-ins/Native%20Plug-in%20Support.aspx
If you are using 2.1.3, are you using the VST or AU version? If I recall correctly StudioOne can host both. We don't test internally on StudioOne, so I can't guarantee that everything works fine, but I know people are using it and we haven't had any complaints.
Please let me know how this works for you.
Dan
