Account assignment mandatory for material

Hi,

While creating contract i am facing this warning message..i can ignore this message , but what is the root cause for it.

Error is :

"Account assignment mandatory for material 100000040 (enter acc. ass. cat.)

Message no. ME062

Diagnosis

There is no provision for value-based inventory management for this material type in this plant. Account assignment is thus necessary.

Procedure

Please enter an account assignment category"

I checked Qty and value update in OMS2 also.

It is maintained.

Then what is wrong?

Uts