Old FileMaker Files did not have an account name. Your converted files do.
Have you tried entering the password twice, as both the account name and the password?
Old passwords were not case sensitive. The Passwords in your new files are case sensitive. Make sure that you capitalize correctly when entering the password, you may have to open the original files and look to see how they were capitalized.
These are the two most likely causes of trouble.
If all else fails, you may want to export the data out of your 2 files into tab separated files and then import the data into a new Filemaker 11 file with the new table option. This will recreate the original table in your new file, but other parts of your original file such as your layout design is not imported. This, however, may not be a major issue as the many changes made to FileMaker from 2 to 11--you may find that you want to redesign the layouts anyway.