Save button grayed out

Using Photoshop CS3 on new iMAC running Leopard. When I go to save an image using the "save as" function, in the resulting dialog box, the "save" button is grayed out. Now if I click and switch from the Adobe dialog to the "Use OS Dialog" then the "Save" button is active again. Any reason for this? How can I fix this?

Thanks,
Andrew

Anyone???????

I dunno, I tested it out on my iMac running Leopard and Photoshop CS3 and all was well.

Do you have all the latest updates? I can't think of a reason why the save button would be grayed out.