Hi again toolexperts - I see what you mean now ;D
You have 2 the same pages; one that works and the other doesn't.
Working:
http://216.75.30.97/work-and-safety-apparel/rain-gear/60-rain-coat/r4160.html
Not working:
http://216.75.30.97/product.php?productid=17345
At the moment I have no ideas what could be causing this.
The only difference between those two pages is that the working one contains this...
<input type="hidden" name="cat" value="326" />
And the one that doesn't work contains no value for cat...
<input type="hidden" name="cat" value="" />
Find out why that number has been omitted and it should add to cart.