From 'perldoc DBI'

Examples of $data_source values are:

 dbi:DriverName:database_name
 dbi:DriverName:database_name@hostname:port
 dbi:DriverName:database=database_name;host=hostname;port=port
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Try as I might, I don't see how: 'DBI:mysql:nikkou6_db:mysql3.freehostia.com' is following that specification.

Assuming (big assumption) that user 'nikkou6_db' has exactly the same permissions as 'root' from the first connect sequence, you may still also have some 'non-local' permission issues for that user within your MySQL permission table. Otherwise, if you intended to connect using 'root' (very bad idea), you also have an incorrect user component in your call.