I used www.mydomain.com/comparison as my Destination URL. When I tested it by searching for my keyword on Google, I clicked the link and it gave me my website's error message. However, When I changed the Destination URL to www.mydomain.com/comparison.htm, the link worked. I don't get it. I can type www.mydomain.com/comparison into my address bar and it works just fine. Why doesn't it work in Google sponsored results? Also, do the two pages have different page ranks? -Thanks-
Your browser has mydomain.com/comparison cached as mydomain.com/comparison.html, so even though you type in the former, it'll go to the latter. When you input your destination URL, you can't use mydomain.com/comparison because it's not a real URL. I suppose you just got confused because it works in your browser. The two pages do not have a different PR because they are both one and the same page.
Yeah when I tested it in AdWords, it worked just fine, but then when I tested the real thing, I got the error message. I think it might have to do with the code following the destination URL.
You can also test your pay per click ads with Google Ad Preview Tool. http://www.google.com/adpreview