Im adding a record using the addnew method but when it reached the update method this error appeared,

"Connection is busy with results for another command". What is the cause of this problem?

This is my code:
Code:
Do While Not rst.EOF  ''' this is tblinv_det 
                    
 	‘’’’some more codes here
                
                Set rstCrdLimit = cnn.Execute(mCrdLimit)
                mRTotal = (IIf(IsNull(rstCrdlimit!amount), 0, rstCrdlimit!amount) + rst!orders )
                
                 
                If rst!acct_no <> invalidacctno Then
                    Set rstcustomer = cnn.Execute("select * from customer where acct_no ='" & mAcctNo & "'")
                    If rstcustomer.EOF Then
                        mContact = rst!contactname
                        mNAME = rst!customername
                        mSTATE = rst!stete
                        mPostal = rst!postal
                   
                        
                    Else
                        mContact = rstcustomer!contactname
                        mNAME = rstcustomer!customername
                        mSTATE = rstcustomer!address1 & " " & rstcustomer!address2
                        mPostal = rstcustomer!postal
                        mCity = rstcustomer!city
                    End If
                Else
                    mContact = rst!contactname
                    mNAME = rst!customername
                    mSTATE = rst!state
                    mPostal = rst!postal
                    mCity = rst!city
                        
                End If
                With Invoice  '''' this is the tblinv_head 
                        .AddNew
                        !ac_no = mAcctNo
                        !inv_no = mInvoice
                        !inv_Date = Date
                         .Update <<====== this is where the error  
                End With
               
                cnn.Execute ("update tblinv_det set  field1= ......" )
                cnn.Execute ("update tblinv_head set field1 = ....... ")
           
       rst.MoveNext
Loop