Oracle Project Billing Issue

Hi All

Please guide me on below mentioned issue

We use Oracle project billing in our Public Sector Environment for managing capital works program. I got a situtation where expenditure line items for any project  some times doesn't appears in draft invoice as line items. I have done everything fronm changing financial tasks dates to budget checks and everthing seems ok. The flip side is we than use manual event to bill those items and than these items may appear when next month billing is performed. Please suggest where can I possible look?

Thanks

Gaurav