I think I may have found a puzzle that this one doesn't solve. (Though it could just be that my implementation is wrong.)
x84|x6x|xxx
x9x|xxx|x7x
3xx|xx2|x5x
---+---+---
xxx|7xx|38x
xxx|2x5|xxx
x27|xx1|xxx
---+---+---
x1x|9xx|xx4
x3x|xxx|x1x
xxx|x1x|56x
I found this puzzle at http://www.websudoko.com