Oracle/PLSQL: ORA-00058 Error

Error:

ORA-00058: DB_BLOCK_SIZE must be num to mount this database not num

Cause:

You tried to start a database whose DB_BLOCK_SIZE parameter value in the initialization file does not match the value used when the database was created.

Action:

The options to resolve this Oracle error are:

Make sure that you are mounting the correct database.
Make sure that you are using the correct initialization file.
You may need to change the DB_BLOCK_SIZE parameter in the initialization file.