Getting a loading icon for categories when adding product [was host problem]

[jjk]

Perhaps investigating the error logs from cpanel would help to identify what in particular is causing the issue on your site.

[GJC Web Design]

better still a cooperative host that is willing to do some digging for you...

[RRPhotography]

Definitely don't have a CDN installed on Joomla, it's just a fresh install with nothing but Virtuemart and YooTheme installed, unless one got installed as part of Yootheme or Virtuemart I dont know about, but I guess it would show up in the modules or extensions menu!

chosen-sprite@2x.png:1 GET http://ryanraymond.co.uk/TestSite/components/com_virtuemart/assets/css/chosen-sprite@2x.png 404 (Not Found)

This is not a problem at all.
The problem is your 503
Perhaps you use a CDN ?

[RRPhotography]

I have done a tonne of background checking and ruling things out and even installing XAMP on my local machine to test which worked fine, as soon as I uploaded it it didnt work?? I sent them everything to do some more digging and told them I had done what they should of done but Fasthosts are absolute dog crap when it comes to support and A2 Hosting were not much good either and said they dont support Virtuemart and told me to come here! even though they are listed at Virtuemart experts and can transfer your site for free including setting up Virtuemart so that was a no go area, I have since gone back to my orignal host because the package I went with A2 only had 500mb of space and 512 RAM on the server and bottomed out when I was just uploading my website which is crap and didnt want to pay more than I do now for a better server, so back to the old hosting provider and no CPanel with that lot!

better still a cooperative host that is willing to do some digging for you...

[GJC Web Design]

Sorry .. at a loss as to what to suggest further .. it works for I suppose 99.8% of  hosts/servers otherwise the forum would be full of complaints.
It has been ajax driven for probably 2 years now..

[RRPhotography]

** RESOLVED **

So after waiting all this time and not hearing a thing from my hosting company and pointing the finger at their servers numerous times it has now been fixed and it was their servers causing an issue and here is their response just in case anyone else ever comes across this on their hosting provider:

"I have checked the thread and I can see that your site was getting rate limited by Nginx Joomla admin, so our engineers have tested joomla burst allowance to prevent pages such as ajax form from being rate limited on the nginx server and monitored. To dig deeper with the process on how they resolved it, we really cannot share it with you on how they had handled the traffic of your website since we have just referred this to their respective department, they have have just sent us a response to let you retest the site from your end and will just refer it back to them once you can still see if your website is still experiencing the same issue."

So there you have it all fixed which I am happy about and had been looking into other options but seeing as this is all setup I will continue to use this system for now.

Thanks everyone for you input and guidance on this it's much appreciated and I hope this answer helps others in future.

Ryan