Search in page redirects Ajax Error

Hi,
On the Page Redirects tab as well as the Captured 404 URLs any attempt to use the search function or change the number of visible generates an error. “Ajax error. Result: “parseerror”, error {}”. Occasionally the error message will be different but it will still be an ajox error. The search function is completely unavailable.

This is true on a number of my sites but not all of them.

I suspect the problem is related to a plugin or two but so far haven’t been able to prove that. In troubleshooting mode, with a default theme and only 404 Solution active the problem remains. The sites in question are pretty active so I can’t just disable all plugins, but I will be setting up a staging site and will find out if actually removing all plugins solves the problem.

In the meantime, is there anything you can offer as a pointer to track down the problem? The lack of a search function is making things very slow and hard to work with.