/apps/perl/5.8.0/lib
...
/usr/perl5/5.00503

That is a red flag (when perl -V:multiarch returns undef). Perl 5.5.x is not compatible with 5.8.x, so any .so files compiled with one perl aren't compatible with the other.

I checked the folder /home/xf023126/lib/perl5/site_perl/auto/HTML/Parser for the Parser.so, and I found it there. I can't figure out why I have a problem?

The error message says it all Parser.so: symbol Perl_Tstack_sp_ptr: referenced symbol not found. It means that Parser.so is linked with a perl (that is linked with a libperl.so ) that defined the Perl_Tstack_sp_ptr symbol, but the perl that is trying to load Parser.so has no such symbol. If you check your libperl.so.5.5 for Perl_Tstack_sp_ptr you won't find it, but you will in libperl.so.5.8. You can't mix your perls like that. You need to make sure the perl you're running your script with is the same perl you compiled your modules with.

PS - ld.so is the dynamic linker/loader.