ok, so i was in CS3 half way, when i get this error message while trying to move a layer.

I must have pressed something or clicked somewhere accidentally.
A quick google search, and i found a reference site, which solve the problem.

Solution: Hit key “Q”. This will toogle to edit in either “Quick Mask Mode” or “Standard Mode”.
I guess most of us work in the “Standard Mode”.

Here’s the difference in your “Tools” palette when in different mode. note the rectangular icon with a circle inside.

Reference:
HELP: Cannot Use Move Tool Because…