Well, what handler are you using to load your code inside mod_perl?!

Have you tested the code in the same machine and Perl without mod_perl? (Probably yes, just to check). Flush the variable $^X when running with/without mod_perl to compare too.

But probably the problem is when XML::Sablotron try to load the XS, and look for the load of new() at new.al! See if the ./auto dir exist in the same path of @INC, for example, @INC has the dir /usr/local/lib/perl5/lib, auto need to exist just after it: /usr/local/lib/perl5/lib/auto.

Graciliano M. P.
"The creativity is the expression of the liberty".