Cost adjustment process issue

Hi All,

We use dynamics NAV 2009 R2,

My client has 3 companies and one consolidated company(report purpose) in the database. 

Data per company filed = NO ,in Item table (27) ,

Items more than 20,000.

Now the problem when run Adjust Cost - Item Entries... report (Finance management)

Some times it wont run.

Then change the Average cost cal.type , item to Item & location & variant   (inventory setup-Warehouse module) and run again.

Then Adjust Cost - Item Entries... report run properly. But the problem is , it takes long time. (4 hours for 3 companies)

Is there a way to avoid this problem ? 

Thanks In advance :) ,

Inventory setup;

Automatic cost posting= Yes

Expected cost posting=Yes

Automatic cost adjustment= Never  (We cant do this Always, because its takes some times at posting each transaction)