I think there is some confusion in this post. Two people replied saying you cannot upgrade to Leopard, but 10.4 is not Leopard.
Now 10.4 is the 1st Tiger release to support Intel, did the Tiger disc come with a MacBook or MBP? If so, this will be your problem, you must purchase a retail version of Tiger.
If it is a full retail version, then can you post more details of the error?