I'm getting some js errors only for some users, and only every once in a while on a page that uses quite a bit of ASP.NET AJAX.

The page also does some intense SQL querying and some string manipulation to highlight text found in the search results.

Could this be a result of performance? Is it always safe to use ASP.NET AJAX in demanding situations or should I be looking to other AJAX techniques?

(By the way the errors I sometime see are):

Message: Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server. The status code returned from the server was: 12031

Message: Sys.WebForms.PageRequestManagerParserErrorException: The message received from the server could not be parsed. Common causes for this error are when the response is modified by calls to Response.Write(), response filters, HttpModules, or server trace is enabled.
Details: Error parsing near ' '.