Based on the KB53878, this particular error was reported when using FireFox which was not a supported browser at that time (ePO 4.0). This should not be the case anylonger.
Which browser version are you using ?
I see. I dont have an ePO 4.6 console handy to test it - please try using a regular supported browser config such as IE 8 or Firefox 3.6 and verify.
I am not sure if Firefox 4.0 falls under the supported configuration. The installation guide only lists four particular browser versions:
Firefox 3.5 & 3.6, IE 7.0 and IE 8.0.
it does work with ie, and chrome with user agent set to either ff 3.x or iex. In ff 4 with agent switcher set to ieX it does not work....
good to know....