Hi Venkata,
Please check what is the field length of AST_STUFE . it could be the reason of overflow.
Also check the note it could help.
Note 869851 - Field overflow with large purchase order quantities
Symptom
When you create or change the quantity of purchase order items with large quantities, a runtime error occurs:
There is an overflow in an arithmetic operation (type P) in program "xxxxxxxx".
Other terms
OKCODE_ADSN, ITEM_PROCESS_MAIN, AD_SERIALNUMBER_IN_PO
SAPMM06E SAPLMEPO
COMPUTE_BCD_OVERFLOW, CX_SY_ARITHMETIC_OVERFLOW
ME21, ME21N, ME22, ME22N
Solution
From now on, order quantities up to an order quantity of 2147483647 are supported.
Caution:
We have since made additions to the corrections in 46C2.