A unclosed div problem almost make me crazy. It is very difficult to track especially when the page is long and complex.
Any suggestions?
I made an online tool called Unclosed Tag Finder which will do what you need.
Paste in your HTML, and it will give you output like "Closing tag on line 188 does not match open tag on line 62."
Update: The new location of the Unclosed Tag Finder is https://jonaquino.blogspot.com/2013/05/unclosed-tag-finder.html