Why do I get a "ORA-01031: insufficient privileges" or "PLS-00201: identifier 'x' must be declared" in my stored procedures?

This fact is documented application developers guide:
 

Privileges Required to Create Procedures and Functions

To create a stand-alone procedure or function, or package specification or
body, you must meet the following prerequisites:

• You must have the CREATE PROCEDURE system privilege to create a
procedure or package in your schema, or the CREATE ANY
PROCEDURE system privilege to create a procedure or package in
another user’s schema.

Attention: To create without errors, that is, to compile the procedure
or package successfully, requires the following additional privileges:
The owner of the procedure or package must have been explicitly
granted the necessary object privileges for all objects referenced within
the body of the code; the owner cannot have obtained required
privileges through roles.

If the privileges of a procedure’s or package’s owner change, the procedure
must be reauthenticated before it is executed. If a necessary privilege to a
referenced object is revoked from the owner of the procedure (or package), the
procedure cannot be executed.

Try this:
 

SQL> set role none;
SQL> "statement you want to test to see if it'll work in a procedure"

If you can do it in plus with no roles you can do it in a procedure.  If you can't, you must have the privelege from a role and hence won't be able to do it in a procedure (unless you are using Invokers rights in Oracle8i.  See the PLSQL documentation for more information on this feature and make sure you understand the ramifications).  To be able to perform that operation in a typical procedure, you need to have that privelege granted directly to you.