Taking off Melchiot for Hasselbaink, fine - but then bringing on Huth for Parker, effectively replacing a decent attacking RB with a out-of-position centre-back who can't cross -
A midfield 3 seems a bit foolish as well, when one is as lazy and/or unfit as Veron
It was the Veron substitution which was the only real mistake. Fixing his inaction and creating an attacking spark was the point of bringing Hasselbaink on; then the loss of Melchiot had to be fixed with a defender coming on. If Gronkjaer was to go off, he should have been replaced with Joe Cole - that way the balance of the team would have been in favour of an attacking midfield, rather than a narrowed, bogged-down midfield.
I actually quite liked the idea of bringing Hasselbaink on after the red card. Ranieri's attacking instincts (at that moment) are a credit to him, I think. Rather than think "right, they are down to ten men, let's just defend the draw to take home, and keep trying to find a way through them as the game becomes a little stretched" (as most managers would have done), he seems to have thought "right, let's try and kill them off." If it had worked, we'd be singing his praises for his courage and daring this morning. And if Veron had been kept off the pitch, it would have worked. So, I maintain, that was his only mistake.