TNS-NAMES error

[CBW]

I have installed Designer 6.0, Developer 6.0 and Oracle 8.1.6 EE (administrator version of OEM) on my Windows 2000 machine. When trying to access Developer I get the TNS names not found error message. I've found 8 TNSNAMES files on my machine. I've changed the data via Easy Config and NET 8 Configuration Assistant. I can't access the OEM console or Developer. I can use SQL*Plus version 3 to access the database but not SQL*PLUS version 8. Any ideas would be appreciated.
Why do I have to use both Easy Config and the Network Administration tool in OEM?

Thanks

[Kishore]

Make sure that right TNS names file is used for the right connection.

Best way is, maintain only one TNSNames file. And do all the entries only in that file. Then you should be able to connect using SQL and OEM