Windows Update Error Code 80244019

Hi, I'm using Windows 8 (not 8.1) on an Acer Aspire V3-571 laptop. I get my internet via the phone line with a TP-Link ADSL modem and wifi-router. I use wifi all the time. For a year and a half since I bought this laptop everything has been fine. I keep my computer clean with Windows Defender, Spybot and Malwarebytes Free. I update them almost every day and run full scans once a week. I haven't had a virus for ages.

But now over the last week or so I get Error Code 80244019 if I try to do Windows Update. I've tried switching off the wifi and using a LAN cable from the router to the laptop, but it's just the same.

But here's the odd thing. I've tried switching off the modem entirely, and, instead, using a plug-in USB modem with a mobile phone SIM card inside charged up with an internet account, and Windows Update works! No problem.

So, Windows Update doesn't like my ADSL modem suddenly after one and a half years of being OK, but, it does like my plug-in USB mobile phone system modem!

I've tried resetting the ADSL modem back to its original factory settings and starting again, but it's still no good. I get the same error code.

Can anyone help?

Thanks!