You have entered a combination of material type and valuation area for the plant that is not defined in the system.
An entry made up of this combination is normally created automatically for all valuation areas in table T134M if you execute the function Edit material type in Customizing for the corresponding material type and then save your data.
The absence of an entry can be due to you setting up and assigning an additional plant to a company code. Although the system then determines the respective company code automatically, it does not create an entry in table T134M for the existing material types in this case.
Contact your system administrator so that the corresponding combination can be entered in table T134M.