Are you certain you have the right code Jim? (daft question I know but the XP key follows same format)
The product key should be 5 groups of 5 each separated by a '-':
e.g. 1ab2b-2ab3b-3ab4b-4ab5b-5ab5b
So the message actually says '1' and '0' (zero) are invalid characters?
Coincidence or not, I have a lot of keys (too many to count) for XP through 2011 plus Office etc, and none of them have a 0,1,L or O.. possibly because they can be mistaken when lower case letters are used?
+1 - I was looking up all my TechNet keys to confirm
Don't think they would be L, I (eye) or O either