two difference query does same job but one work and other not

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PowerShell

I am working on two different query does same thing but one query fails after running powershell twice. First query:

'{0,-59}{1,20}' -f "DROP table $worktablename",(Get-Date -Format yyyyMMdd:hhmmss);
try {
INVOKE-SQLPLUS -MESSAGEONFAIL 'DROP WORK TABLE FAILED' -QUERY @"
SET SERVEROUT ON;
SET TERM ON;
SET TIMING ON;
SET SERVEROUTPUT on;

WHENEVER SQLERROR EXIT SQL.SQLCODE;
EXEC DROP TABLE $('amiuser1.$worktablename');
COMMIT;
"@
@"
try { $null = Execute-NonQuery-Oracle "DROP TABLE $('amiuser1.$worktablename')" 
} Catch { } Finally { }

But running following query works everytime :

'{0,-59}{1,20}' -f "Create work table WRK_UCMU073_SU_EDIT_DETAIL",(Get-Date -Format yyyyMMdd:hhmmss);

Invoke-SqlPlus -MessageOnFail 'Create work table WRK_UCMU073_SU_EDIT_DETAIL failed' -Query @"
SET PAGES 60;
SET LINES 170;
SET ECHO ON;
SET serveroutput on;
WHENEVER sqlerror exit sql.sqlcode;
EXEC drop_work_table('WRK_UCMU073_SU_EDIT_DETAIL');
create table amiuser1.WRK_UCMU073_SU_EDIT_DETAIL as
select * from SU_EDIT_DETAIL where 1 = 0;
grant select on amiuser1.WRK_UCMU073_SU_EDIT_DETAIL to misdev;
commit;
"@