Was this payment part of a large batch to HMLR? You can check this by clicking double-clicking on the posting on the matter ledger, then clicking on the Allocations tab. If any of the other matters on this payment batch have been billed, then you would be unable to reverse any partial payments,
To get around this, you can either:
To credit note the supplier and credit the matter ledger:
From the DPS home screen select Purchase Ledger.
Select Disbursement Invoice.
Post the opposite of your original posting, in the Net box enter the value as a negative figure.
Go to Purchase Ledger.
Select Pay Supplier, then pick up the credit note and Post.
To credit the matter ledger only:
From the DPS home screen select Client Postings.
Select General postings.
Select type as DPU.
Complete fields, enter the Net box as a negative figure, and Post.