Not sure what version though and the remote has finally given up the ghost after a three year assault by my youngest so Iuntil the replacement arrives I won't be able to find out if I am running the latest version or not.
The WebIF and custom firmware offer two "soft" remotes through the browser, one suitable for phones, the other for PCs and tablets, and the Settings tab of the WebIf lists the custom firmware version. If you have neither of these facilities on your box then the version you're running is certainly not the latest. Mine shows:
Custom Firmware : v 4.1.3
Web Interface : v 2.87
The Humax keeps falling off the network and I don't know why. It connects via a home plug normally but sometimes the network connection just stops for months at a time before randomly coming back at some point. I have tried plugging an ethernet cable directly into the router with no luck.
Is that no luck in getting anything working, or no luck in fixing it if it's dropped off via the HomePlug?
Easy/obvious ones first. Connecting the box to the network involves an Ethernet cable in the back of the box connecting to a router, or to (presumably) the same router via a HomePlug. When you look at the Ethernet port at the back of the powered-on box it should have one steady light on the left (as you look at the back of the box) and a blinking one to the right when traffic is passing. The router should have similar lights. Are they on? Have you tried changing the Ethernet cable(s) in case they're faulty? Have you tried a different port on the router in case it's faulty? (Unless you have implemented VLANs or mappings/NAT based on the physical port then you should be able to swap adjacent cables on the router's LAN ports without affecting things.)
If all the cables are OK, the lights are lit and all these physical signs seem right, what does the box's Network screen look like? What's its IP Address, subnet mask, router address and DNS address when it works or, if it's not working, what are those settings when it's not working? What are the equivalent settings on the PC with which you're trying to contact the box? Is the box's IP Address set manually or by DHCP? It could be that the box's Ethernet is fine - technically it's OK at OSI Layers 1 and 2 - but if the IP Addressing is wrong then it may not be able to talk to the rest of the network. If you accidentally have two conflicting DHCP servers running on the network this could happen, or if you have manually set a static IP and subnet mask on the box while everything else uses DHCP and the DHCP changes, this could also have the same effect.
Finally, if all that looks good, check your router for some esoteric setting that may be causing issues, such as MAC-address filtering that's throwing away all the box's traffic before anything sees it.
Diagnosing network connections can get quite tricky, but I hope the above helps pinpoint the problem before trickiness needs to be involved.