Money 2003 will not open a file created with a later version. It will give a bogus password error if you try to do that. THat is what you are describing.
If you have a *.m11 file on your drive, that is a copy of your Money file when a later version converted your file. Money 2003 can read that file.
I wonder if you tried Money Plus and found that it only works with US, and maybe Canadian, Money files.