[rdiff-backup-users] ImportError: /usr/lib/python2.4/site-packages/rdiff_backup/_librsync.so: wrong ELF class: ELFCLASS32

[Kannarat Chiemchitvanicha]

I just installed rdiff-backup and trying to run this simple backup command. 
     # rdiff-backup /mnt/hdb1/tmp /mnt/hdb1/lost+found

This following is the output I received

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Traceback (most recent call last):
  File "/usr/bin/rdiff-backup", line 20, in ?
    import rdiff_backup.Main
  File "/usr/lib/python2.4/site-packages/rdiff_backup/Main.py", line 25, in ?
    import Globals, Time, SetConnections, selection, robust, rpath, \
  File "/usr/lib/python2.4/site-packages/rdiff_backup/SetConnections.py", line 30, in ?
    import Globals, connection, rpath
  File "/usr/lib/python2.4/site-packages/rdiff_backup/connection.py", line 534,
in ?
    import Globals, Time, Rdiff, Hardlink, FilenameMapping, C, Security, \
  File "/usr/lib/python2.4/site-packages/rdiff_backup/Rdiff.py", line 22, in ?
    import os, librsync
  File "/usr/lib/python2.4/site-packages/rdiff_backup/librsync.py", line 27, in
?
    import _librsync, types, array
ImportError: /usr/lib/python2.4/site-packages/rdiff_backup/_librsync.so: wrong ELF class: ELFCLASS32

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I'm not sure whether the question mark ? after 'in' indicates an issue or is it supposed to be that way?
Also I have a big problem regarding the share library '_librsync.so'. 
I tried to do some search on this and found no solid answer. 
However, it seems like I have a problem with the 32-bit/64-bit mismatch and I need to relink the library in the 64-bit mode.
Could sombody please confirm if this really is the problem and provide a detail solution? I am a linux newbie...