Very Annoying PHP Errors

[Peter Pluta]

I recently upgraded to 5.2.1_1. After upgrading (or before not exactly 
sure) I began getting errors ALERT - canary mismatch on efree() - heap 
overflow detected in my Apache logs. Also, certain parts of one of my 
database (mysql) driven sites stopped working. Certain pages just 
stopped working, they return a blank white page. I'm absolutely stumped 
on what it could be. I have tried recompiling php 4-5x with different 
options and re-installing apache etc... Nothing is working. I looked for 
php bug reports, and found this one http://bugs.php.net/bug.php?id=40119 
but it does not really pertain to me. Can anyone give some pointers or 
tips on what to do?

Right now I am thinking of just downgrading to PHP 5.2.0 because that's 
what worked last. Is there an easy way to downgrade ports?

Any feedback, tips, or help would be greatly appreciated.

Thanks,
Peter