The more I look into this, the more I'm worried that it's a bigger issue that others just haven't run into yet.
Similar issues have been seen with other products admin control panels, listing several different causes, from mod_security to something within the response from the server (
http://drupal.org/node/40805)
I'm not sure what I have to do to try and track down the cause.
I guess a good place to start is:
Corexian, do you remember the last things you changed and saved? Maybe between the two of us we can narrow it down.
The error is basically that your browser is telling the server 'I don't know how to handle that type of file.' -- Almost all browsers are set to accept all types tho ("*/*").
Zanix, if you're checking in on this thread, I'm willing to provide
ANY Information (including passwords if needed, if it will help others) to you to figure this out. I can make changes directly to the database, but that's kind of annoying. Also willing to jump through any 'try this' hoop to see if we can figure out what's going on.
I'm sure Corexian and I aren't the only ones seeing this - but as a lot of people don't generally use the config panel after initially setting up...