Oracle Errors Interview Question:

ORA-12505: TNS:listener does not currently know of SID given in connect descriptor?

Submitted by: Administrator

Cause: The listener received a request to establish a
connection to a database or other service. The connect
descriptor received by the listener specified a SID for an
instance (usually a database instance) that either has not
yet dynamically registered with the listener or has not been
statically configured for the listener. This may be a
temporary condition such as after the listener has started,
but before the database instance has registered with the
listener.
Submitted by: Administrator