dc42:
The usual culprit is the LiquidCrystal library, which has a totally unnecessary "begin" call in its constructor, taking 60ms to execute (longer than the longest available watchdog interval).
Did you mean "longer than the TWO SHORTEST available watchdog intervals"? The interval an be set as high as 8 seconds:
#define WDTO_15MS 0
#define WDTO_30MS 1
#define WDTO_60MS 2
#define WDTO_120MS 3
#define WDTO_250MS 4
#define WDTO_500MS 5
#define WDTO_1S 6
#define WDTO_2S 7
#define WDTO_4S 8
#define WDTO_8S 9