invalid ELF header

[mslinn]

I'm running Ubuntu 9.04 64bit on an Intel Core 2 Duo.

$ pdftk
pdftk: error while loading shared libraries: /usr/lib/libgcj.so.90: invalid ELF header
$ ls -alF /usr/lib/libgcj.so.90
lrwxrwxrwx 1 root root 16 2009-05-09 19:48 /usr/lib/libgcj.so.90 -> libgcj.so.90.0.0
$ file /usr/lib/libgcj.so.90.0.0
/usr/lib/libgcj.so.90.0.0: data

What should I do?