Simple Thoughts Blog had a sporadic but consistent comment problem. On submitting comments a blank page was occasionally returned instead of the original page with the comment added. How did I debug it?

First I wanted to reproduce the error consistently. I could very rarely see this error with my Firefox browser, possibly because I remain logged in most of the time and/or cookies. So I opened Internet Explorer and cleared the cache. I created a test post and started adding comments.
I was lucky. The bug was consistently reproducible in Internet Explorer. All I had to do was refresh as post page (posting to wp-comments.php) and a blank page would be returned. My first job was done.

BTW: In the process I discovered a stupid bug in WordPress' implementation of first time moderation. It is purely email based.

Next I had to go in the code to find out the exact location of the error in wp-comments.php. However before I did that I wanted to remember which plugins hooked into wp-comments. The only one was wp-hashcash, an excellent comment spam prevention plugin.
So before going further I disabled the plugin.

Voila, the error was gone. I was using a really old version of the plugin, probably 1.5. So I tried upgrading. However it started spewing strange database errors. So I decided to keep it disabled for now.

Now my blog is more vulnerable to comment spammers. However it will not prevent legitimate commentators from commenting anymore.

Thanks goes to James Huff, who kindly pointed me to this error for the second or third time. I couldn't let it pass anymore thinking it was only occasional or postpone it for the next version of the site.