I am hard at work on the new issue of Creative COW Magazine and have a drop-to-printer date of the 1st on Thursday. I really don't have time right now to go to the manual and figure out what's up but I am getting a dialog box telling me that I have more than 10 spot colors and so InDesign can't do a print preview.
It tells me that I have to remove spot colors and as I used a previous issue as my template and am just replacing and moving things around for speed -- I am sure that I have colors that I can safely remove that herald back to the last issue.
In the flyout menu of the swatches palette choose "select all unused", then click the trashcan in the swatches palette to delete them.
If there are still some colors left over that you are not using, you may have them specified as spot colors in you placed graphics. You will need to then open them in your grapahics program(most likely illustrator, as few people know how to spec a photoshop job with a spot color), and delete the colors form the swatches palete of your graphics program. InDesgin will then allow you to delete the swatch in InDesign.