If activity has been posted to the General Ledger, the record will not be able to be deleted.  There is a journal entry in the ledger that must have a source record.

Set user preferences to show the deleted/voided entries:

 

     

    1. From the main menu bar select Tools, Options.
    2. Select the Record tab.
    3. Highlight Activity from the left navigation bar
    4. Mark the Show deleted and voided transactions checkbox.
    5. Click Ok