Purchase order status is Waiting

HI All,

Here i have one query regarding Purchase order.

I am trying to post the Invoice for Purchase order then system is throwing one warning message saying One or more Packing slips can not be selected.

Then i went to the below path and deleted the Waiting status line against the PO.

Accounts Payable-> Inquiries-> History ->Purchase orders-> Invoice

In the above path the PO was existing with Waiting status then i deleted that line and i could able to invoice the PO later.

But My query is why it is going for Waiting status and when it will go. And let me know when it will have the Executed status.

Regards,

Sathish kumar