Error is fairly straight forward. In order to install libapreq-1.33 you need a lower version of mod_perl. mod_perl 1.99 was beta for mod_perl 2.0 and you should be using libapreq-2.0 or higher with it. mod_perl also modified its API during the 1.99 cycle so if your running Apache2+ (whcih I assume you are since you have mod_perl 1.99) do yourself a favor and get the latest mod_perl (2.02 I think) and then the latest libapreq (2.07?). After that HTML::Mason will install properly.