This issue seems to be the result of a change as of version 22.214.171.124 where we url encode non ascii chars by default. So what happened is the encoded url is too long. In the past the only thing that caused path too long exception were malicious requests so we automatically ban the ip address.
To solve it:
1. Comment out the BannedIPBlockingHttpModule in 2 places in Web.config to disable it temporarily.
2. Go to Administration > Advanced Tools > Banned IP Addresses and find your ip address in the list and delete it so you are no longer banned.
3. Add this to user.config <add key="AlwaysUrlEncode" value="false" />
4. Any pages tyou created after upgrading you may need to go to page settings and change the url and also may need to find the encoded url in Url Manager and delete it.
5. After everything is working again uncomment the BannedIPBlockingHttpModule so it works again.
See this article for more info http://www.mojoportal.com/non-ascii-urls.aspx
Ironically this change was made to fix a problem with Persian Urls but it seems to be causing more problems than it is fixing so I will change the default from true to false for AlwaysUrlEncode in the coming release
Hope it helps,