Photoshop CS3 crashes when I try to deactivate it

Question

I will deactivate and delete Photoshop CS3 (10.0.1 German) and then install Photoshop CS5.
I use Mac Pro Early 2009 and Mac OS 10.6.3 (German).
When I start the deactivation (menu help) Photoshop crashes directly.
I have start the Mac with Shift-Key; I have started it as root; I have checked the disk permissions. No success.
Here a part of the alert "Photoshop quiet unexpectedly":
Exception Type: EXC_BAD_ACCESS (SIGBUS)
Exception Codes: KERN_PROTECTION_FAILURE at 0x0000000000000000
Crashed Thread: 0 Dispatch queue: com.apple.main-thread
Can everyone help me?
Apart from that Photoshop works fine without any problems.

Answer 1

Thanks for the replies.
I understand now that the procedure is probably the reason.
I was just experimenting as LAB colours are colours we see through our eyes, while RGB, CMYK etc are "computer" colours and so I use LAB colours a lot, before switching back to RGB.
I normally switch to LAB mode and click on the Lightness channel, then play with adjustments of that channel. This time I decided to mess around and see what would happen if I removed all channels except the Lightness one....
Converting to greyscale for me is not enough unfortunately and LAB B+W provides much better contrast and tone than hitting CTRL+Shift+U to greyscale.
Again, I understand what you say, my point being though that Photoshop should not crash because I incorrectly remove the channels, perhaps a warning to tell me I can't do it would be better.
I'll pass this onto Adobe anyway.
cheers