yes michel,
it was be , but sorry cant be of help never had a ninja, never used a ninja
but cfr i find excellant , now i have used the correct tools ,
thanks to mike haliday loan of upholstry tool ( must get one )
and mike, take the batteries out?

what if i forgot to put back in

consequenses could be disatrous.
and no was the switch tripping, just plain going off.
sound like dereks initial answer was the most likely .
geoff