This is a typical forum post that makes us look like we don´t answer.. yet this customer was answered immediately when they sent a support ticket.
But they fail to delete the forum post so people still think no one answered...
So I will answer again here...
The problem is you didn´t read the "REQUIREMENTS" which is stated clearly on the reservation manager page.
It is NOT made to work on Joomla 1.5+
Resman pro however will work.