dezl0ck

Either update your server or grab this plugin.

https://josephscott.org/archives/2009/03/wordpress-libxml2-episode-iv-a-new-plugin/

Since it was a 406 it appeared to be more server side than anything else. After contacting tech support they informed me that they’re blocking the request due to some security risks. After looking at their logs it does appear that mod_security is thinking that the bookmarklet is malicious.
From Tech Support:
this is because the authors of WordPress are using some malformed URL requests that are frequently used for cross site scripting attacks. I checked the security logs and your requests were indeed logged and flagged.
Please contact the authors of WordPress and submit a bug report for their application. They might even apply you with a patch. From our experiences of dealing with them, they are quite open for suggestions and bug reports.
Here is an excerpt of our security log:
========================================
Request: xxx.xxx.xxx.xxx – – [07/Dec/2004:16:01:32 -0600] “GET /wp-admin/bookmarklet.php?text=&popupurl=http%3A//www.domain.com/wp-admin/edit.php&popuptitle=WordPress%20%u203A%20Viet-Justice%20%u203A%20Posts HTTP/1.0” 406 271
Handler: application/x-httpd-php
—————————————-
GET /wp-admin/bookmarklet.php?text=&popupurl=http%3A//www.domain.com/wp-admin/edit.php&popuptitle=WordPress%20%u203A%20Viet-Justice%20%u203A%20Posts HTTP/1.0
Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Accept-Encoding: gzip,deflate
Accept-Language: en-us,en;q=0.5
Cache-Control: max-age=259200
Connection: keep-alive
Keep-Alive: 300
Referer: https://www.domain.com/wp-admin/edit.php
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.5) Gecko/20041107 Firefox/1.0
Via: 1.1 thor.atlantagothic.net:3128 (squid/2.5.STABLE6)
X-Forwarded-For: 172.16.xxx.xxx
mod_security-message: Access denied with code 406. Error normalizing REQUEST_URI: Invalid URL encoding detected: invalid characters used
mod_security-action: 406
HTTP/1.0 406 Not Acceptable
Connection: close
Content-Type: text/html; charset=iso-8859-1