Epson WF-3720 two-sided printing greyed out/grayed out

Thanks. I contacted Epson, as you suggested and their response solved the problem. In case it helps anyone else, Epson said:

Can you please follow the steps below.

1. Click the Apple icon and then click on ‘System Preferences’. Click on either ‘Print and Fax’, 'Print and Scan' or 'Printers and Scanners'.
2. I would advise you to remove the printer from the printers list and then re-add it. To remove the printer, in the printers list, highlight the printer in the printer list and click the [ - ] delete button. Ensure the printer is turned on and click the [+] and choose 'Add Printer or Scanner'. If the printer is detected, it will be listed in the Add screen. It will state 'Bonjour' for Wi-Fi or 'USB' for USB connection under 'Kind’. Please also ensure the 'Use' option lists the printer name and not Airprint.
3. Make sure it does no say Airprint next to the word KIND, below options and supplies when the WF-3720 is selected. If it does, then make sure you download and install this: http://download.ebz.epson.net/dsc/du/02/DriverDownloadInfo.do?LG2=EN&CN2=&DSCMI= 56427&DSCCHK=dc633cf7207148c4dfb70dd3985ff1b680f9c090
4. Then follow Step 2 again.
5. Then follow the steps in this guide: http://kb.epson.eu/article.aspx?article=4605&p=7

If you require further assistance please do not hesitate to contact the Epson Customer Inter@ction Centre and we will endeavour to resolve any further queries you may have.

Thanks for your reply, but this is what I have already tried several times. Re-setting the printing system simply means deleting and reinstalling the printer driver. I have noticed the two-sided printing option is available in Preview, but it is not in Pages. So perhaps the problem is with the Pages app?

Thanks, but there is only one checkbox in the Print dialogue and it is greyed out.

Thanks. A discussion at the Epson community suggests the problem is with the Mac rather than the printer. Hence this query.