bcp in of datetime type data results in an "Invalid date / time format"
I have seen this before.  Ensure your datetimes are formatted like this:

yyyy-mm-ddThh:mm:ss

Example:

2011-01-18T17:30:59 would represent January 18th 2011 at 5:30:59PM

It has been a while since I ran into an issue similar to this, but I remember this being a step I took to resolve my problem.