If I recall correctly (and I very well may not), this is the annoying error that you get under 8i (and possibly other versions), when trying to connect to a remote database that you've defined under 'ORACLE_SID'. It won't work... you have to place the SID in 'TWO_TASK'.

For the original poster -- If you can't get a response from tnsping, then track down your DBA... this is just the type of thing that they hate dealing with, but the reason why they can justify getting a big paycheck. (there are a whole lot of things that can cause this error)