I just checked the search folder, and it contains remains from an old plugin version, incorrectly installed.
Please FULLY re-install Ajax Search Pro using the plugin manager first and apply the fix I have recommended. (deactiavate, delete and install from codecanyon archive) It won't work with old plugin versions. If it's still won't work after re-installing, then I will of course take another look.
If you downloaded the plugin previously before purchasing from a 3rd party site, then I recommend to check your installation for viruses and backup everything. Pirated copies are very dangerous, and most likely contain malicious code to steal your website credentials.
Let me know if reinstalling and trying the modification didn't work.
Also, make sure not to use the Index table engine, the modification (id search) will only work with the regular engine.Best,
If you like my products, don't forget to rate them on codecanyon :)