Ubuntu – Repeated ‘authentication required’ for wifi

I recently upgraded to 14.04 and over the last few days, I'm having frustrating problems while connecting to my home wifi network, one I've been connecting to without a problem (with earlier Ubuntu versions) for over a year. Windows computers and Android devices have no trouble connecting either.

The problem is that whenever I connect to the network and enter the correct password, it tries connecting for a little while, and simply gives the the 'Authentication required' dialog box again.

I have a Lenovo Z400 laptop (wifi works perfectly on Windows 8 on the same machine, by the way), and a Linksys EA4500 router.

The 'wireless' page in the router configuration looks like this (SSID and passphrase removed): http://imgur.com/0PWHRpo.

sudo lshw -class network

*-network
       description: Ethernet interface
       product: RTL8101E/RTL8102E PCI Express Fast Ethernet controller
       vendor: Realtek Semiconductor Co., Ltd.
       physical id: 0
       bus info: pci@0000:02:00.0
       logical name: eth0
       version: 05
       serial: 20:89:84:f1:32:3c
       size: 10Mbit/s
       capacity: 100Mbit/s
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress msix vpd bus_master cap_list ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=r8169 driverversion=2.3LK-NAPI duplex=half firmware=rtl_nic/rtl8105e-1.fw latency=0 link=no multicast=yes port=MII speed=10Mbit/s
       resources: irq:42 ioport:2000(size=256) memory:d3404000-d3404fff memory:d3400000-d3403fff
  *-network
       description: Wireless interface
       product: Centrino Wireless-N 2230
       vendor: Intel Corporation
       physical id: 0
       bus info: pci@0000:03:00.0
       logical name: wlan0
       version: c4
       serial: 68:17:29:be:21:2f
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress bus_master cap_list ethernet physical wireless
       configuration: broadcast=yes driver=iwlwifi driverversion=3.13.0-24-generic firmware=18.168.6.1 ip=192.168.1.149 latency=0 link=yes multicast=yes wireless=IEEE 802.11bgn
       resources: irq:46 memory:d3500000-d3501fff

sudo lsusb

Bus 002 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 004: ID 0bda:0129 Realtek Semiconductor Corp. RTS5129 Card Reader Controller
Bus 001 Device 003: ID 8087:07da Intel Corp. 
Bus 001 Device 005: ID 046d:c077 Logitech, Inc. 
Bus 001 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 002: ID 13d3:5170 IMC Networks 
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

also, during while trying to connect, dmesg | grep wlan0 tells me I've been deauthenticated from <address> (Reason: 2).

I've also tried deleting all my saved networks, reboting and then reconnecting, which sometimes works, but sometimes doesn't.

Can someone please tell me why this is happening, and what I can do to fix it?