Tricky DNS problem

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yaho_

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Location
Dublin, Ireland
... well, I think so anyway.

Problem: The website I manage is periodically down - but not for everyone at the same time, i.e. it might be accessible in the US and on some ISPs here in Ireland, but at the same it won't be accessible via a different ISP's connection here, say). Not just an ISP issue though. Not exactly this problem either.

Details
* We switched our hosting from one company to another about 8 weeks ago, but the registration is still with the old host.
* We launched a new site about the same time - in fact, as soon as the new host's nameservers were in control of the domain.
* After the switch, the old host had retained an old C-NAME record. They deleted this over 4 weeks ago though.
* When it's down, ping/nslookup fail to find the host or claim a non-existant domain. Generally the non-www version of the URL could be pinged (see below) but essentially there seems to be some error resolving the DNS.
* Looking at our new host's error logs, I can see that the requests aren't getting as far as their servers. They've also tested this for me.
* Last week, I copied the site to a new webspace on the current host's servers (shared hosting btw) with a new IP. The problems reappeared this morning.
* The old site had only been accessible through the Example Web Page URL but the new one was set up to be accessible through both. When the site was down, it used to still be partly accessible through the non-www domain (never associated with the old IP address). i.e. it found the new nav and displayed it almost in text form but couldn't pull the CSS, images, etc. from the www domain. This wasn't the case this morning though.
* I mentioned ISPs above but only as an example - the problem isn't limited to our ISP. It's not limited to our office network either.
* Our office LAN (or at least some machines) were connecting to the web using outdated DNS servers that our ISP upgraded from some time ago. This has now been updated and obviously the problem reappeared this morning.
* Our email still goes through the old host.


Any ideas?
 
Seem to have solved this with help from someone on another board... in case there's a similar problem again, the issue seems to have been at the TLD level - one of the designated nameservers for the TLD (.ie in this case) somehow still listed the old nameservers as being in control. Those in turn thought that the www version of the URL didn't exist, hence the lack of a pattern to the outages in terms of ISP, times of day, etc.
 
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