problema con cursor

hola

tengo el siguiente problema al ejecutar un cursor:
Server: Msg 16929, Level 16, State 1, Line 21
The cursor is READ ONLY.

el cursor es el siguiene

DECLARE @doc varchar(255)
DECLARE @AUXdoc VARCHAR(255)

DECLARE CR CURSOR FOR
select doc
from tmp_cartera_rep order by doc

set @AUXdoc = '0'

OPEN CR
FETCH NEXT FROM CR
INTO @doc

WHILE @@fetch_status = 0
BEGIN
IF @AUXdoc = @doc
BEGIN
DELETE FROM tmp_cartera_rep where current
of CR
where Current of CR
END

set @AUXdoc = @doc

FETCH NEXT FROM CR
INTO @doc
END

CLOSE CR
DEALLOCATE CR
GO


gracias por su colaboracion
.