This issue diagnosis is unconfirmed but various reports of WICReset problems and successes offer some clues about when/how the Workforce 840 can be successfully reset by the WICReset tool.
The WICReset tool cannot successfully reset the waste counter in a way that survives a power cycle (ie: power on/off) if the printer has already been reset using the appropriate IPR tool provided by Epson America.
The IPR tool (accessible by providing a valid Serial code for your printer) does not reset the waste counter more than around 40% (leaving the counter at around 60%) and cannot be re-used.
To date one WICreset user appears to have been able to successfully reset their waste ink counter if no other tool has been used/attempted previous to the WICReset usage.
Note of Caution:
The above is just a theory at present and based on minimal results to date. It would be useful to confirm or discount the single success so far if any Workforce 840 owner has a printer that has not yet had any attempted reset using any other tool. Please contact OctoInkjet for more information if you are in a position to help.