My friend’s computer had the error message that said: “This application has failed to start because MFC71.DLL was not found.” whenever she tried to start Photoshop CS3, and this affected the way plug-ins ran (in some cases, they wouldn’t run or display at all).
To solve this, just grab the MFC71.DLL at http://www.dll-files.com/dllindex/dll-files.shtml?mfc71 and put this DLL file into the same directory as Photoshop (you should see a whole lot of other DLLs in there).
Start up Photoshop after that and voila – no more error message, and all your plugins should show up correctly now.