asset purchase error

I try to pay down payment for asset, f-90, special GL:A, system says error:

Posting key 31 does not permit specification of a special G/L indicator

Message no. F5761

Diagnosis

Posting key '31' and special G/L indicator 'A' were transferred.

System Response

Inconsistent data cannot be prcessed.

Procedure

Remove the special G/L indicator online.

If the data comes from another application, the consistency of the data there must be guaranteed.

how to resolve?