I'm having a similar problem and was wondering what, if anything, you've found out?
I can only spend approx. 10-15 minutes on my site before I'm blocked. I found out i had some type of virus/trojan or whatever, now its removed and I still get blocked super easy.
I have just the same problem. Traceroute outpu that my ip is being blocked just one server prior to my target server. I whois that server and emailed the support people.
Then thing is that whenever I get allowed at my target site I can access but they need to add me explicitly to the allow file on the server.
Any idea how that happens?