Ajax not supported?

I have a page that uses an AJAX request (using Prototype's Ajax.Request()) to validate something. We keep very detailed logs of all of the requests. Occasionally customers will complain that they are entering something and it is not being validated. In such a case I check the logs searching for their IP address, time of their email, and a description of the information that they tried to have validated.

Sometimes I find that they are not in the logs, which would imply that the AJAX request is not executing.

One example of the most recent case of this has a user string of

Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; GTB6; InfoPath.1)

according the email they sent.

I cannot find them in the log. Is there any reason to suspect that somebody using IE8 would not be able to execute AJAX?

Is there any practical way that I could alter my environment to not support AJAX as well to test some alternatives.

Note this most recent user said that they have tried many times over multiple days so it's not like this is a one-time thing for them or a bad connection, necessarily.

This is a regularly occurring issue that I cannot recreate. Any hel开发者_开发技巧p would be appreciated. Thanks.

A couple things immediately spring to mind:

1. They may have JavaScript disabled
2. It might be timing out.

I know when I've been on a bad connection I've seen Ajax stuff fail, and I close out of the site, and I bet it shows up on the logs similar to what you're seeing.

Does the user have some weird toolbar running? Or maybe some other extensions which might disturb your XMLHttpRequest object, or the Microsoft variants of it?