Comment 16 for bug 1408963

Exactly the same being seen here, frequently.

Vivid 15.04, upgraded on release from 14.10 (previously upgraded several times)
Intel 3945ABG using iwl3945
Dell Latitude D830

deauthenticating by local choice message in dmesg, followed by a dozen or so lines of "Failed check-sdata-in-driver check, flags: 0x4" all timestamped within 0.01 seconds.

Check network-manager - networks all shown. Turn wireless hardware switch off, all go. Back on, all stay gone.
Restart network-manager - "Wi-Fi Networks: device not ready"

Under 14.10, on first booting the machine, it would always associate with a weaker wireless network, and need manually changing to the stronger. This never happened prior to 14.10, and doesn't happen under 15.04

Time before failure can be several days, or (as this morning) can be ~20min after boot. It can fail to resume, or it can happen whilst the machine's in use. I think I've had it a dozen or so times since upgrade.