One time when I encountered this after a reboot of the device, being a Cisco router or Switch or Wireless Device, I get back to factory settings. After some research I found out that the device is bypassing the startup configuration. This is what you get after a reboot:

--- System Configuration Dialog ---
Would you like to enter the initial configuration dialog? [yes/no]:

To fix this answer no to the question and press enter and type the following.

enable
show version

If you notice Configuration register is 0x2142 in the information displayed, then type the following

enable
configure terminal
config-register 0x2102
end
reload

And when asked if you want to save the configuration, type no

Some other Configuration Register codes and what they mean. The list below have been taken from the Cisco website.

0x0000-0x000F | Boot Field Parameters 0x0000 Stays at the system bootstrap prompt 0x0001 Boots system image on EPROM 0x0002-0x000F Specifies a default netboot filename.
0x0040 | Ignore NVRAM contents.
0x0080 | OEM bit enabled to exclude details in boot messages.
0x0100 | Break disabled
0x0400 | IP broadcast with all zeros
0x800-0x1000 | Console line speed
0x2000 | Boot default ROM software if network boot fails
0x4000 | IP broadcasts do not have net numbers
0x8000 | Enable diagnostic message and ignore NVRAM contents