Package hyperref Warning: Height of page (\paperheight) is invalid (0.0pt),
(hyperref) using 11in.
Obviously your class doesn't define \paperheight, so you have to do it by yourself or rely on defaults.
For example, to get A4 paper, use:
\setlength{\paperheight}{297mm}
\setlength{\paperwidth}{210mm}
For letter paper:
\setlength{\paperheight}{11in}
\setlength{\paperwidth}{8.5in}
Underfull \hbox (badness 10000) has occurred while \output is active
Underfull \vbox (badness 10000) has occurred while \output is active []
Have a look at: What are underfull hboxes and vboxes and how can I get rid of them?
LaTeX Warning: 'h' float specifier changed to 'ht'.
You used a placement option h for a float (table or figure). If LaTeX cannot place it right there because of too less space, it moves it to the top of the next page and issues that warning.
Usually h is too strict. This way you don't allow top, bottom or page placement. Use at least ht instead, or relax it to htbp or even !htbp if you like. If you really need it to be exactly "here", use the H option together with the float package. There are further ways. But adding placement options is usually fine.
geometrypackage defines a lot of such sizes, and I guess most people just use that, if not class options. – Stefan Kottwitz Dec 12 '10 at 20:17