Error : xml request error proxy error

It's a network problem and you need to talk to your IT guys in the office. In general, it sounds like your HTTP requests leave your office, bounce off the ISP router and go back into the office, but get lost on the way back. Try accessing the site hosting FCKeditor through a Windows machine name or IP address (one of those 192.168.x.x or 10.x.x.x) and see if this fixes the problem.