Error loading /usr/lib/postgresql/plpgsql.so

Hi,

I've recently upgraded a test server from postgresql 7.2.2 to version
7.3.2, and also rebuilt perl 5.8.0 on a gentoo linux system. Restoring the
databases worked fine, selecting from tables works fine, but a simple
insert statement generates this error:

ERROR:  Load of file /usr/lib/postgresql/plpgsql.so failed: /lib/libc.so.6: version `GLIBC_2.3' not found (required by
/usr/lib/postgresql/plpgsql.so)

The same error is generated whether the insert is done from the psql prompt or through a perl script using DBI and
DBD::PG(latest versions of both). 
The insert statement is:

insert into testrun(f1, f2, f3, f4, f5, f6, f7 ) values( 'aa', 'bb', 'cc', 'ddd', 'eee', 'ffff', 'ggggg') ;

(with actual field names and values altered)

The testrun table has a trigger that runs before insert or update, that calls a plpgsql function. This is evidently
wherethe problem is. However, 
/lib/libc.so.6 clearly exists, and my current version of glibc appears to be 2.3

What's the best way to go about fixing it?

Thanks,

Wes