"Execute immediate" problem

[thomasp]

declare
.....
begin
for x in (select table_name from cols where column_name = 'ID_CTLGRP' and table_name like 'TUA%') loop

dbms_output.put_line ('Processing Table:'||tabs.table_name);

execute immediate 'Update '|| x.table_name ||' set ID_CTLGRP = REPLACE(ID_CTLGRP,chr(39),''_'')'||' WHERE ID_CTLGRP LIKE ''%''%''';

End loop; --tables
dbms_output.put_line ('Job Complete');
end;