Createlang error installing SQL-Ledger

I'm trying to install SQL-Ledger on a Mandrake 10.0 box, but I get the
following error

[root@localhost sql-ledger]# su postgres
[postgres@localhost sql-ledger]$ createuser
Enter name of user to add: sql-ledger
Shall the new user be allowed to create databases? (y/n) y
Shall the new user be allowed to create more new users? (y/n) y
CREATE USER
[postgres@localhost sql-ledger]$ createlang plpgsql template1
createlang: language installation failed: ERROR:  could not access file
"$libdir/plpgsql": No such file or directory
[postgres@localhost sql-ledger]$

I have checked all requirements, and google cannot find anything to help me.
The faq at sql-ledger also doesn't help.

Some info:

[postgres@localhost sql-ledger]$ cd $libdir
[postgres@localhost pgsql]$ ls -l
total 12
drwx------  6 postgres postgres 4096 Apr 24 15:40 data
-rwxr-xr-x  1 root     root      338 Apr 24 15:16 initdb.i18n
drwx------  2 postgres postgres 4096 Apr 24 15:16 tmp
[postgres@localhost pgsql]$


What can I do to resolve this?

Thanks

Roland