that is either a bug, or you're not using the module code you've shown above.
try to make sure you're using exactly that module (by adding a print into the module body).
or do this:

print join "\n", @INC;
print "$INC{'CWI/Message.pm'}\n";
[download]

in the script, and tell us the full path of CWI/Message.pm and if there are any other CWI/Message.pm files lying around your file system.
another question, what happens if you explicutly use use CWI::Message qw(get_msg);?