Database Link Problems

I have created a Database Link from SQL+Worksheet and DBA Studio and no mater what, I can't get the stupid thing to work. Can someone tell me why I'd get:

"TNS-12640 Authentication adapter initialization failed"

when I try to retrieve rows from the Database Link? Thanks, Jeremy

Post your CREATE LINK syntax and your select statement with error message(s).

P.S. Change the passwords before posting...