Since the error message does not contain information about ajax search pro files, I'm not able to tell what might cause this. As described it sounds like a missing file, but strangely it works when the plugin is disabled. The search plugin loads almost nothing on the editor pages to prevent any possible issues, so this might be somewhere in the initialization script.
I've installed the ithemes exchange free version on my test site, but I can't find any shortcodes to test or use. I have to see or re-create the issue to suggest a solution, it can be literally anything. Do I have to enable a core add-on?
If you can provide temporary FTP and back-end access to your test server when I can debug the problem, that would be the best possible solution. I would probably find and fix the cause as well. I'm not sure if I can re-create this on my test environment.Best,
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