Moisture on basement walls?

I have a 3-year-old home with an unfinished basement. We have four foot cement walls with four foot kneewalls insulated with R20 batted insulation. We did have this vapour barriered but in September 2008 we had to remove the insulation and vapour barrier due to extermination. We did not replace the vapour barrier. We do have a 12-hour wood stove for our main source of heat, which is loacated in the basement. Our home is approximately 1200 square feet on both the main and basement. We have a Venmar Constructo 1.0 (air exchanger) that was installed three years ago. Just recently we noticed that our walls in the basement are always damp with moisture. In many places there is water dripping/running down over the walls behind the insulation. What would be the cause of this? Any suggestions would be helpful. On the outside walls of our cement walls, we have styrofoam insulation. On the remainder of our home we have Tyvec and vinyl siding. We live in Atlantic Canada so weather wise, it's typically 15 - 25 degrees celsius summertime and anywhere from 0 to -15 degrees celsuis wintertime. Please offer any advice or suggestions on what could possibly be causing this dampness in our basement.