I just had the same with my new FSX-PC (Win7) and its client (still running XP). Bought FSUIPC4 and WideFS7 today new, no connection, whatever I tried...
I renamed the whole workgroup, ran the diagnostics, released folders with any properties and everything. I read the WideFS-Manual over and over and almost got nuts about it, because the network itself worked and I could see any PC and read and write in any every released folder. Just the same error in the log like above by trying to connect my FSX with the client via WideFS.
My last idea was to set the servername and protocol in the [config] section of the .ini...nothing. And now in the middle of the night (I hate unsolved problems and can't let it go, whatever it will cost) I won the war against my network...I had to change the servername with its IP-adress 192.168.x.x
FSX with WideServer: 1 connected :D :D :D
Obviously there's any translation-mistake in the router the reason for that strange behavior...just keep in mind if that happens to the next one!