Datablock and procedure in forms 6i

hello,

i tried to insert data into datablock through the procedure in forms 6i.
i got error as
****************************
FRM-30433: Query procedure should have only one argument of type
REFCURSOR/TABLE and its mode should be IN OUT.
Block: BLK_DISPLAY
Procedure: GETDATA
FRM-30085: Unable to adjust form for output.
****************************
the steps i have done is
(i) i have written a procedure "GETDATA" in program unit
and is compiled without any error.
(ii) i went to the datablock property in which
     (a) Query data source type = Procedure
     (b) Query data source name = Getdata
     (c) Query data source column = i have given all the coloumns
            which have been selected using query (which i have
         written in the procedure GETDATA).
     (d) Query datasource arguments= i have given paramters which are
         in and out parameters of the procedure GETDATA. For example
         in the case of "IN" parameter
         i have given the parameter name in the 'Argument Names". in
         the value column i have given the text item name as
         :blk_display.txt_empno with corresponding type and mode.
         i have left blank for the Type Name.
what could be the error??