Error: Delta Initialization using flat files

Hi

I am doing "dditive Delta Process for flat files" and m facing a problem...this is the scenario:

I created an infosource first with UPDATE TYPE(under transfer structure)later i created an ODS with some infoobjects and later activated ODS.

Then Created the updated rules for this ODS with the infosource i created.

But there i can see only 2 options :Overwrite and No Update...But i cant see "Addition" option .

Plz tell me whether i shud get this option there if s how to get???

eventhough i continued loading data...

then later i am loading a flat file and with the option

"initialize delta process" when i click on start i get a messege:

There can only ever be one active delta load per combination:

InfoSource / source system.

A second delta initialization deletes old delta tables in the OLTP

The last initilaization of the delta transfer was by InfoPackage

IP_GR_Additive_Load On 16.05.2006 At 12:02:52

Do you want to undertake a new initialization ?

and if i click on yes then i get the following error messege:

Delete init. request

REQU_366LZ2308N03N165CWLVIHBCH before running

init. again with same selection

Please give me the solution...

if possible give me the steps to do it.

Tanks,

Vijaya