Error: "ORA-00903" when trying to get Explain plan. (4325610)

When a SQL statement is executed ,    Error:  "ORA-00903" is returned  when trying to get Explain plan.

SOLUTION 1:
Is the SQL-Statement itself executable?

This error means that the table name specified in the statement is not valid, it probably is a reserved word.

===> Action: The options to resolve this Oracle error are:

Rewrite your SQL to include a valid table name. To be a valid table name the following criteria must be met:
* The table name must begin with a letter.
* The table name can not be longer than 30 characters.
* The table name must be made up of alphanumeric characters or the following special characters: $, _, and #.
* The table name can not be a reserved word.

SOLUTION 2:  
If missing the Explain plan table, please go to:
View | Toad Options | Oracle | General
and check
Explain Plan | Table for TOAD_PLAN_TABLE