I received technical advice on this issue from two apple support people, one of whom treated me like an idiot, the other of whom couldn't resolve the issue and then on my third phone call I was put through to a Level 3 (senior technical person) who said this connectivity problem was due to too many people on other wireless networks in my area being on the same channel and the only solution was to find the person who the wireless network belonged to each time and get them to reset their router to a different channel! I said that this was not a practical solution and he replied that unfortunately in built up areas, this now happens. I explained my friend had an apple macbook air and was in the same room as me and could connect to all three wifi networks we had access to and he replied that as mine was a different model (macbook pro retina) it had a different wifi card and so could not be compared to hers. He had no other solution for me other than to contact each router owner whenever I wanted to connect to wifi and had difficulties and get them to change their channel number.... seriously!
Fortunately I found this thread and all was resolved in a few instants (after about 2 days lost productivity due to no internet). I called Apple to lodge an official complaint as to why three different apple technical support people did not give me this solution as I was prepared to have to completely wipe my computer so it went back to the original operating system (even though the level 3 guy had said this would make no difference as this issue was due to the wifi in my macbook pro, and nothing to do with Yosamite).
I'm not a technical person and do not understand how apple are not advising people of this work around for people who have upgraded from their original operating system to Yosamite at their first point of contact. Thumbs down to Apple on this and thumbs up to whoever came up with this solution. Thankyou!
