I was doing some rust removal on the underneath right hand side yesterday, and when finished I attempted to start the car.
Loads of error messages came up on the dashboard - Suspension failure - Electrical failure - Gearbox failure - Incorrect part fitted - Engine failsafe mode.
At first I thought I had accidentally severed a wire as there was a big harness near where I was working, but it transpired that I had tripped the IFS (Inertial Fuel Shutoff) when I moved the carpet. Resetting the switch put everything right.
An error message saying 'IFS tripped' would have been nice!

 

Rust you say, in England..... never.