The co-administrator of one of my wikis seems to have been suddenly blocked from all access to anything to do with Wikidot.com about 2 hours ago (as of this timestamp). I fear that perhaps his IP address might have been added to the Global IP Block List mentioned in our sites Site Manger pages, but there seems to be no way to check the Global IP Block List.
This person is in no way, shape, or form a spammer of any sort. I've advised him to send an email to your support address, but in the future is there some way to troubleshoot issues like this by checking whether somebody has been added to the Global IP Block List before bothering Wikidot support?
More information on this problem. I had my partner do a traceroute from his computer, and compared it to a traceroute from my own computer (I can successfully see all of wikidot.com, but he cannot).
It looks like your wikidot.com servers are hosted by some 3rd party datacenter in Dallas, TX, USA. In my successful traceroute to our specific wiki URL, the destination machine is as2-1.s.wikidot.com, and the router immediately before it is po1.fcr03.dal01.dallas-datacenter.com. (And there are a few more dallas.datacenter.com router hops before those last two.)
In my partner's traceroute, he's getting 100% packet loss at the next hop immediately after po1.fcr03.dal01.dallas-datacenter.com, which means his ping packets (and all other packets, apparently) are being rejected by as2-1.s.wikidot.com. But all my packets, including ping packets, are getting through to that server just fine.
This would seem to conclusively indicate that either his specific IP address or perhaps a subnet address that contains his specific IP address is being globally blocked by wikidot.com. He's on a Verizon network in New Jersey, USA. Did you recently add some Verizon subnet to your Global IP Block List to deal with some spammer originating from that network?