This is why continuous integration is such an important (and great!) thing.
The old mantra of 'works fine on my machine' - something I used to hear a lot in the days of WINNT 4,SP1,2,3,4,5,6, ADO 1, 1.5, 2,
When you're at the customer site and they're all looking at you wondering,
'General Exception 0xC00005'
'what does that mean' ??!
'It means I'm going to go back to the office and kill somebody'