Hi,
In my D60 Manual it has the Err asking you to depress the shutter again and if that don't sort it contact your local Nikon dealer.
This is probably the same for yours as you've stated as much.

There is a reset switch on the D60 which should be on the D40 also, Which is used to reset the camera but you will loose anything not written to the card it resets the camera to default settings and the clock/Date will need to be set again.

Lookup in your user manual index "Reset Switch" and see what it says..;)

Have to tried removing the Card & Battery and popping em back in again to see if that cures her tantrum ??

It's gotta hurt your Nikon not working properly....