Have you recently added a new Adobe plug-in? Like Mask Pro or something? As Fred has pointed out a few times, Mask Pro (and probably other plug-ins) causes a conflict with Flexi. You'll have remove plug-ins one by one until you find the one that causes the conflict; or rename your Plug-In folder in Adobe to xPlug-In, or something like that. Then change it back each time you want to use the plug-ins in Photoshop.