PL/SQL :: Killing And Dropping Users Connected From Application

I have a data base for the bank application development. So there might be more than one sessions of the application running on the data base as well as there might be more than one data base sessions being connected from the dbas.

There is refresh procedure to refresh the data base from the baseload scripts ,So for that first we need to disconnect the users (Kill the sessions) and then drop the users then recreate the users and populate the users with the base load data.

I have prepared the killing and dropping user script in the following manner, Most of the times it is working fine and killing the users but some times it is not able to kill the drop the users it is erroring out with the error that can not dorp the users as there are active sessions running ,

set termout on
set echo on
spool Kill_sessions_drop_users.log
DECLARE
v_alt_stmt VARCHAR2(1000) := 'ALTER SYSTEM DISCONNECT SESSION ''';
v_kill_stmt VARCHAR2(1000);
[code].......

--This will kill all the sessions except the current session

CURSOR cur_usr_dtls IS SELECT username FROM all_users WHERE username IN ('ACTIVITI','TP','TPCORR','TPTUX','TPVIEW');
v_dr_stmt VARCHAR2(1000);
BEGIN
EXECUTE IMMEDIATE 'ALTER SYSTEM ENABLE RESTRICTED SESSION';
DBMS_OUTPUT.PUT_LINE('The database has been put in the restricted mode');
FOR v_cur_ssn IN cur_session
[code]........

--Here we are making the processor to wait for 60 mins so that that the killing will happen at the OS label

DBMS_LOCK.SLEEP(60);
FOR v_cur_usr_dtls IN cur_usr_dtls LOOP
v_dr_stmt :='DROP USER '||v_cur_usr_dtls.username ||' CASCADE';
BEGIN
EXECUTE IMMEDIATE v_dr_stmt;
[code]........