It seems the problem is the CellSize.
Your Solid Obstacles are 32 X 32 Size.
If you increase the CellSize value it becomes impossible for Enemy pass trough some certain points of your map.
And if you Set the CellSize value lower of 32 X 32 it will touch the corners.
The best way that I realized its to set the CellSize in 32 X 32. But it still touchs a little bit. <img src="smileys/smiley19.gif" border="0" align="middle" />