ora - 24372

Hi guys
What this error is?

SQL> DESC DBA_TABLESPACES;
ERROR:
ORA-24372: invalid object for describe

Thanks

Here is the error description

ORA-24372 invalid object for describe
Cause: The object to be described is not valid. It either has compilation or
authorization errors.
Action: The object to be described must be valid.

Hi guys
I am trying to run form6i. When I used Datablock Wizard
to enter the table name, I am getting ORA-12154: TNS: could
not resolve service name.
Could any one tell me why I am getting this error and how
to resolve this.

Thanks