i use gl ap ar oe and ic modules. the cost method is moving average and "allow negative inventory levels" box is checked on IC option.

when i make sales invoiec or credit/debit note entry on OE module, i find under invoice tag, unit cost column Some times the amount is zero or blank; some times unit cost column shows up amount. Both of them are inventory items. I don't know why.

(the "allow nefative inventory levels" box is checked, the reason is I receives products and make sales invoices first,  then later make purchase on ap. because issue the sales invoices every day but enter the purchase once a week).

What costing method do you use?

 moving average method

Does that item have a total cost?

 No there is no total cost column. but there are sales unit price, sales quantities, sales total amount columns

Not in O/E, in I/C.  Run the I/C Item Valuation report and see if that item has a total cost.

I run the item valuation on IC and i can see each item has actual cost, most recent cost, total quautity  stocking unit, avg unit valus etc. some items quautity is zero, some are negative 

If you have an actual cost and a positive quantity at the time the line item is entered, then an average cost item should have a value in OEORDD.UNITCOST.

 So if actual cost and quantity is zero or negative, the OEORDD.UNITCOST should be zero? Does OEORDD.UNITCOST zero effect company cost good of sold acct and inventory? 

Of course.  That's why you should never allow negative inventory when you use average costing.

 my company asked accpac consultant to set up accpac program and the cost is very expenses. Acccording your expenses which method is better if i want to allow negative levels on ic modules?

Standard cost.

 i read the help for standard cost. it said:

Standard costs are carefully predetermined target or attainable costs that are useful in building budgets and gauging performance. You might use this method if your item costs do not vary much.

Now my company inventory item more that 1200 and purchase price change frequently. Do you think standard cost still is a best method?

 more information about standard cost method:

Warning!  If you ship units of an item for which you have not yet entered a standard cost, Inventory Control calculates the cost of goods sold using a standard cost of zero.

that meaning if i received the products, shipping them and make sales invoice first, then after a fews days i record purchase on accpac program, the cost of goods sold amount will be zero on OE?

Very true.  Either way you go, you need to have discipliine in the accounting department, and procedures that are followed by the users.