No Ethernet connection between Router and Dell E6440 via Dell Docking Stati

Has anybody here come across the issue where there is no ethernet connection between a router and a specific laptop (or model number?) whilst in a Dell docking station? Full details below:

Equipment/Setup

1. Dell Latitude E6440 running Win7 64bit PRO (yes I know, Win7)
2. Dell Advanced E-Port II Replicator Docking Station
3. ASUS DSL-AC68U Wireless Modem Router with latest firmware
4. Ethernet Connection in laptop, Intel I217-LM, Driver version 12.13.17.4, Date 04/08/2015
5. Cat 5E cable ~1.8m (6ft) long. Different cables have no effect.

Operational background

1. Direct Ethernet cable between router & Dell E6440 functions, as does WiFi.
2. Previous router via Docking station, there is ethernet connection.
3. A Dell E5470 in the docking station, there is ethernet connection.
4. Via Device Manager (in E6440), Intel Ethernet Connection I217-LM Properties Link Speed with Speed & Duplex in Auto Negotiation, Diagnostic tests manly failed. Hardare Passed. Identify Adapter option has left hand LED blicking at Ethernet Socket on Docking Station.

So, the question is, what settings do I need to get my Dell E6640 in the the Dell Advanced E-Port II Replicator Docking Station to have an Ethernet Connection with the Modem Router?

Thanks for your attention.