Why won't my camera allow me to change playback std?

I was viewing an HDV tape and when I change to a DV tape the option to change playback std is greyed out. Why is this?

What do you mean to change playback? You can't change it from standard to anything else because it's standard definition tape, with a standard definition signal. If you've recorded in HDV on a standard def tape, you should be able to, however as the camera will play in both HD or SD depending on the TV being played on.

So, try resetting the camera. This is a fairly easy procedure which involves either going into your setup menu and choosing "reset" (or intialize), or, removing the batteries for a few minutes. It may be that the firmware loading got corrupted and the camera just needs to be "rebooted," which is something that turning it on/off won't accomplish. But after which, you should have the camera reset to factory default settings.

Another tip is to go to Canon's website and look for firmware updates. Download and install them.

Thanks. I meant change the camera so that it will playback a tape recorded DV, as opposed to HDV. But the answer is, apparently, turn the camera off, pop the tape, put it back in and try again. Repeat if necessary. I wish there were a better answer though...

Well, sometimes tapes recorded on other mediums can be problematic for certain advanced features like that one. My recommendation would be to simply burn to DVD and watch that way.