If you haven't rebooted your computer since the problem first occurred reboot your system now, then do a full VST Rescan.
Sometimes the VST Scanner gets stuck and if that is part of the problem until you kill the process or reboot things won't change.
To perform a full VST Rescan:
1. Go to Edit > Preferences > File - VST Settings.
2. Under Scan Options, select Re-scan Existing Plug-ins and Re-scan Failed Plug-ins, then click Reset.
3. The following confirmation message appears: “This will reset configuration settings for all your VST plug-ins to defaults. VST Plug-ins will be unavailable until a VST Scan is performed. Any custom configuration settings will be lost. Are you sure you want to do this?”
4. Click Yes.
5. Click Scan.
The background VST scanner scans your list of plug-ins. When scanning is complete, you can reapply any custom settings to your plug-ins.
Note: After performing a full VST rescan, clear the Rescan Failed Plug-ins and Rescan Existing Plug-ins check boxes, especially if Automatic Background Scan is selected. Leaving all of these options configured simultaneously can lead to a continuous scan loop.
TheSteven's post in trouble w/ loading VST was marked as the answer