I have the same problem since ~ 2-3 month:
- not able to autoconnect to wifi
- old connection worked well (until I did't tried edit to test) but any new one don't.
- not depend on the wifi type...tried many, even a pure unencrypted wifi.
- be able to connect with manual connection, so the settings must be proper...
- to find the solution I fumbled my wife's unused N9 from the drawer...but get the same symptoms! :/
- reflash not solved the problem! :/
- at first time when switch to auto mode, it try connect and for 1 moment it seemed woking but than fall back to manual mode.
So I checked my AP-s log: http://pastebin.com/twDVVL5F -> If I have right, the n9 drop the connection, but I don't know why :/

I have no other idea... If anybody has, please share with me/us! Thanks in advance.