If you have an Open Item for either a Grant or an Admin voucher, and you wish to change the payment option from ACH to Check (or Check to ACH), you will need to find the voucher on the History tab in AP and uncheck (or check) the ACH box. 

If the ACH box is grayed out and can’t be modified, then the ACH option on the Grantee or Vendor was previously unchecked.  

To allow you to modify the checkbox:
  1. Change the ACH option on the vendor or grantee back to ACH;
  2. Uncheck the box on the voucher in AP (you may need to refresh);  
  3. If you don't want to use the ACH option for this grantee or vendor in the future, then you'll need to go back and turn off the ACH option on the grantee or vendor record after changing the voucher.