Error in All Purchase Order

Good Morning,

While opening All purchase order i am getting the following error

"Cannot read a record in Purchase orders (PurchTable).
An unsupported NULL value has been selected from the database.

[Microsoft][SQL Server Native Client 11.0][SQL Server]Changed language setting to us_english.

Cannot read a record in Purchase orders (PurchTable).
An unsupported NULL value has been selected from the database.

Microsoft][SQL Server Native Client 11.0][SQL Server]Warning: Null value is eliminated by an aggregate or other SET operation."

Please help me.

Regards.