Pattern Maker Greyed Out

Hi I'm on CS3 and the Filter>Pattern Maker menu item is Grayed Out ie I can't select it. I've tried the few things I can think of. Anybody come across this – what am I missing?

ps Plugin is in the correct Folder.

I know how to do it manually but that takes quite a while so, please help.

Have you moved anything from the default installation location or created any subfolders to hide the Photoshop folder? Is your file 8-bit or 16-bit? RGB or CMYK?

Yes Remon, you got it in one. 16-bit. I don't know how it got there as my new files usually start 8-bit. Thanks.