Ajax Javascript Errors and random 404s

Looking for a very experienced AJAX, PHP, Javascript programmer, who's extremely experienced in debugging. I'm getting this error once in awhile and I can't figure out why. Error: the xajax Javascript file could not be included. Perhaps the URL is incorrect? URL: content/ajax/xajax_js/[login to view URL] Also, if you go here: [login to view URL] You will get this error: error: 'navigator is undefined Code: 800A1391 Source: Microsoft JScript runtime error. I don't know if this is the cause of my 404s, but, I also have a [login to view URL] error I see once in awhile. On line 747 on [login to view URL] which says: $row = mysql_fetch_array($result); The 404 is caused by an extra word inserted into the URL of a correct URL: For Example, if the correct URL is: [login to view URL] the 404 will appear because the cart will do this to the URL: [login to view URL] This happens for my product pages and catalog pages randomly. Need to fix ASAP. Thanks ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Deliverables must be in ready-to-run condition, as follows? (depending on the nature? of the deliverables): a)? For web sites or? other server-side deliverables intended to only ever exist in one place in the Buyer's environment--Deliverables must be installed by the Seller in ready-to-run condition in the Buyer's environment. b) For all others including desktop software or software the buyer intends to distribute: A software? installation package that will install the software in ready-to-run condition on the platform(s) specified in this bid request. 3) All deliverables will be considered "work made for hire" under U.S. Copyright law. Buyer will receive exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). ## Platform IE, firefox