Make sure the Green battery Light is illuminated when pugged in and battery is fully charged. If the battery light is amber color, then the battery is charging and the light will eventually turn green. Sounds like your battery is failing or the power cord may have an intermittent break in the circuit.
The message is generated by the low battery alarm monitor and will shut down the Netbook to protect itself. Try removing the battery and running the machine on the power cord only to see if the condition repeats itself.
The battery alarm message is generated and can be changed in the power options properties. Start>Control Panel >Power Options.