Yes they are. I have them connected to a wireless router and have also tried connecting them directly to the modem/router. Everything else on the network works fine. Both machines can see each other and access & transfer files ok. As a side note (not sure if this relevant) this issue first occured after I noticed MM had crashed on one of the machines saying it couldnt find the 'coinconfiguration' file. It had obviously failed to also restore the file from backup so I had to end task and relaunch the program. It was at this stage the visibility disappeared from both machines. A complete uninstall (deleting the directories in local & roaming folders) failed to fix the issue and a complete rebuild of one has also failed to get them talking. I'm thinking this has to be some 'network discovery' issue though everything else on the networking side of things works fine 

Yea I can see both machines in mobileminer both from my laptop and my phone. Its just the programs dont see each other. I've just updated both machines to MM v3.2.2 & recreated the Homegroups on both machines but still no go. Got me totally miffed atm...

I know that occaisionally mine will drop a system off MM panel even though everything is ok.  I have not had them drop completely though like you have where they do not come back.

I have never had a problem where my GPU rigs do not see each other.

As a possible fix do you all have the latest .NET installs and updates?

Yes, both machines are win 8.1 running the same version of .net -  I also installed MM on a laptop thats also on the network (as a test to determine if the issue is with either of my mining machines), and it doesnt see the other machines either and vice versa. I'm curious as to how MM 'detects' other machines on the network running the program now.

I have been getting API errors and .NET crashes. I will update in the morning and poke around the settings.
Windows 8 gave me issues awhile back when using MultiMiner but that was many revisions ago and W8 not 8.1.

That could be it or a system driver not up to date with 8.1.
So much fun with windows updates.   

Ok, so since sorting out the Multiminer 'networking' issue I've now started noticing the program occassionally stops responding if I click between the 2 machines from within the program. The only solution I've found so far is to 'end task' and then everytime I restart it I get the following message:

"Multiminer has detected running miners that it does not own - did you want to kill them?"

I click 'yes' to this and the program relaunches fine with the miners still visible. Anyone else seeing this issue?

I know they are working on it.  Nate was not given one when they first came out to get support ready.
He has stated in the thread he has a Zeus/GAW miner coming so he can add support.
There is a fork of BFGMiner you can use that does allow it to work but it is not official yet.
Here is the thread that has the link.
https://bt.irlbtc.com/view/644921.0
Just replace the BFGMiner folder in you MultiMiner folder and it should work.

For some reason Fury Support is now broken.  I cannot run any of them.
I am sure it will get straightened out soon.