if you tell us the exact message it gives you when you try, we will be able to offer more help. or if you read the message yourself, you might even figure it out.
for example, some potential messages are "it appears magic alone won't hold these ingredients together", "you appear to not have enough of one of the ingredients", "you would need 540 manapoints to make that item", "the ingredients appear to be in the wrong order", etc
also, if you'll mention what you're trying to make, and where you're trying. and as a last resort, make sure that you have the ingredients in the right order, and that you type the right numbers of each ingredient beside them.
--jason