unixODBC fails to open psqlodbcw.so library on Mac OS X 10.4

Hello everybody out there using psqlODBC,

On Linux, Windows and Mac OS X 10.6, I could get psqlODBC working perfectly fine.
However, on a Mac Mini with PowerPC running Mac OS X 10.4.11, isql fails to open the psqlodbcw.so file, which I
installedusing EnterpriseDB's PostgreSQL Application Stack Builder: 
MacMini:~ user$ isql -v my_dsn
[01000][unixODBC][Driver Manager]Can't open lib '/Library/PostgreSQL/psqlODBC/lib/psqlodbcw.so' : file not found
[ISQL]ERROR: Could not SQLConnect
However, the file exists with global read, write and execute permissions:
MacMini:~ user$ ls -l /Library/PostgreSQL/psqlODBC/lib/psqlodbcw.so
-rwxrwxrwx   1 root  admin  2006960 Sep 26  2011 Library/PostgreSQL/psqlODBC/lib/psqlodbcw.so
Moreover, all required dependencies of the library are present on the machine:
MacMini:~ user$ otool -L /Library/PostgreSQL/psqlODBC/lib/psqlodbcw.so
/Library/PostgreSQL/psqlODBC/lib/psqlodbcw.so:
        /usr/lib/libltdl.3.dylib (compatibility version 5.0.0, current version 5.4.0)
        /usr/lib/libssl.0.9.7.dylib (compatibility version 0.9.7, current version 0.9.7)
        @loader_path/libpq.5.dylib (compatibility version 5.0.0, current version 5.4.0)
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 111.1.4)
        /usr/lib/libiodbc.2.dylib (compatibility version 4.0.0, current version 4.17.0)
        /usr/lib/libiodbcinst.2.dylib (compatibility version 4.0.0, current version 4.17.0)
        /usr/lib/libgcc_s.1.dylib (compatibility version 1.0.0, current version 1.0.0)
Could you please help me to find additional diagnostics to run in order to pin down the problem?

Thanks in advance,
Julia