No NOCD even?
I had this problem some time ago, though I got kicked way more often.
What has happened was that my water.dat had corrupted itself, yes, it corrupted without me touching it.
At first, it started with me being unable to see when I was in a tunnel, a week or so later and I got kicked every time I tried to enter.
If you have the DVD, do a clean reinstall, Uninstall, delete folder, install.