I have my late 2013 Macbook Pro since March. I was able to connect to 3 different networks at home without a problem from almost any place for 4 months. Suddenly, I could not connect to any network after "sleep". I solved it partially doing what was recommend in this case: SMC Reset, Set Service Order, Delete "SystemConfiguration" Folder, Turn Off Bluetooth, Disable Keychain Sync, etc. I said partially successful because I could not connect to a particular network (Network6) from a particular point (Point6) even if I did it flawlessly every day for 4 months and other devices (Dell laptop, iPad and iPhone) DO connect to that network at that point.

I can connect to that network from other places, but not in that Point6, where I usually work.

Setup: I have a Linksys WRT54GL Router (Network1) with a Hawking Technologies HiGain 300N Range Extender (Network6), both firmwares up to date. Point 6 is less than 2 meters away from the Range Extender and I never had any issue there. Now, sometimes I cannot see that network, or if I see it I cannot connect, or if I can connect there is no internet access, even if there is an acceptable good signal, signal to noise ratio and low interference. Also, from that Point 6 I can connect to Network 3 that is more than 35 meters away and other devices can connect to Network6. I had reset the Range Extender 6 times and nothing. I have analized my home with Netspot Pro and there is very good Signal to Noise Ratio in Point6, very low noise and no interference with my neighbors networks because they have different channels: I am the only one who uses channel 6, they use 1,2 or 11.

So far I have concluded that:

1) It is not a hardware problem because my Mac does connect to other networks and to Network 6 from other places but not from Point6 where it connected every day many hours for 4 months. (I am writing this connected to Network 6 in the basement and the Range Extender is in the floor above me; very good STN Ratio).
2) It is not the Range Extender or Network 6 because I can connect to Network 6 from many other places farther away and because other devices connect to Network 6 in Point 6.
3) It is not Noise or Interference in Point6 because a) Netspot detects the same acceptable level of noise everywhere, b) No interference from neighbors networks in that place (I am the only one in channel 6) and c) Other devices connect to Network 6 in Point6.

As I wrote, I have deleted the SystemConfiguration folder many times but nothing. It does not connect to Network 6 in Point6.

Any suggestions will be appreciated.