Delta extraction not working

Hi all

I have a question on delta extraction. I initialised the first extraction for the DS 2lis_11_vahdr and to test the delta process created a few sales orders after that. and when i check in RSA3 in the OLTP sys. it shows the number of records as in the initialised state the newly created records are not shown in the total numbers.

i also tried a delta extraction from my BI system and it shows teh number of records extracted as 0. But if i delete the extract structure in and fill them again the number of records now is increased.

is there any setttings that i have to do either of the systems to get the delta process going?

Thanx in advance

Sujai