Screen Copy to Clipboard producing Empty Clipboard

I'm sure it's here some where... I wish there was more sorting the forums by subcatigories.

My issue:

When I "copy picture of selected area to the clipboard" [Cmd+Optn+Shift+4] in photoshop (cs2) it often* just clears the clipboard.
At times I'll copy an area of the screen and it works, I'll CMD+N a new doc, it will give me the clipboard size, and paste properly. If I the try another capture it will make the camera sound and on CMD+N open a document the same size as the previous capture, and then past nothing (paste is grey).

Any Ideas?

On a Quad G5 4+gigs, everything updated.

*Intermittent behaviour, and I can't find a pattern. Seems to do it less when it's a small section of the image, and all the time if it includes the whole image.

I've seen that also, but the only thing I can tell you is I stopped pasting to the clipboard because it got annoying. Next time it happens, try going to Preview and "create new from clipboard" to see if that works, or just view the clipboard in the Finder to see if the shot actually took. Either of those choices will at least tell you if the shot is being taken in the first place, and that the problem may be with Photoshop.

Well I've found a work around - just make sure photoshop isn't the front app (itunes floating player is handy for this).
Feels like a security thing to me (securing what from whom, I have no idea).