When I logged on as Instance owner and issued command below, I got error.
db2 connect to FEDDB user newuser1 using pass123
When I 'su' to the user newuser1 on AIX, I was able to connect database without problem.
> db2 connect to Feddb
Database Connection Information
Database server = DB2/6000 8.2.2
SQL authorization ID = NEWUSER1
Local database alias = FEDDB