I am running a PHP site that uses Ajax and jQuery as well. The site will run fine for quite some time, and suddently my pages (and ajax-retrieved sub-pages) comes back with
After some research I think this may be the solution (Taken from http://bugs.php.net/bug.php?id=28929 ):
[2010-06-11 15:12 UTC] in2ishun at yahoo dot com ***************** SOLUTION!!!!
I realize this issue is AGES old, but it still manages to be the top hit on Google searches as of now (6/2010).
I fixed my own instance of seeing this error. W2k3, IIS6, PHP 5.2.6, MySQL 5.1.
The problem is in the pathing. When I used the MSI installer for MySQL without doing an "advanced" installation (where I could manage the install details), it added a path to the system environment that contained spaces. Even after changing the path environment to use the Windows short-name location of the mysql bin directory, it still didn't work.
The solution was for me to reinstall mysql and set the default installation path to just off the root (e.g. C:\mysql). Once I did that the error went away and my app started working.
There are a number of sites with a variety of potential solutions to this issue and several of them mentioned paths and the "libmysql.dll" file (in the "bin" directory of your mysql installation).
If this helps you solve your problem, consider leaving a comment here so others can see that it works.