SQL & PL/SQL

Hi,

I am trying to execute below statement but got the error:

exec dbms_stats.gather_schema_stats(
ownname => 'nascto',
estimate_percent => dbms_stats.AUTO_SAMPLE_SIZE,
method_opt => 'for all columns size auto',
degree => 7,
options => 'GATHER AUTO')

ORA-00900: invalid SQL statement
The statement is not recognized as a valid SQL statement. This error can occur if the Procedural Option is not installed and a SQL statement is issued that requires this option (for example, a CREATE PROCEDURE statement). You can determine if the Procedural Option is installed by starting SQL*Plus. If the PL/SQL banner is not displayed, then the option is not installed

When I checked this below query: it is showing banner for PL/SQL

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle9i Enterprise Edition Release 9.2.0.1.0 - Production
PL/SQL Release 9.2.0.1.0 - Production
CORE 9.2.0.1.0 Production

TNS for 32-bit Windows: Version 9.2.0.1.0 - Production
NLSRTL Version 9.2.0.1.0 - Production

I am puzzled ,now what to do ?
Does anybody have any idea,Please let me know.

Thanks.