Looks like the module (XML::Parser) has been installed in the 5.8.0-site tree, and that directory is in @INC — which is not a problem in and of itself. Rather, the problem likely is that the dependent libexpat (C) library cannot be loaded, for example because it simply isn't installed.  So that would be the first thing to check.

P.S. anything else after the

...0509-022 Cannot load module /u/unilocal/perl-5.8.0-site/lib/aix/aut
+o/XML/Parser/Expat/Expat.so ?...?
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that would hint at why it cannot be loaded?  Often, you'll find the underlying system error there, e.g. "No such file or directory", "Permission denied", or some such.