I have a site that keeps displaying an "Unkown Error" when I try to upload an image (see attached). I assumed it was a permissions issue, but when I run the sitescan.php script it takes me to a couch page with an error that says Page Not Found and this is what I see for URL when the error is thrown: http://site123.com/<br%20/><b>Notice</b>:%20%20Use%20of%20undefined%20constant%20REQUEST_URI%20-%20assumed%20'REQUEST_URI'%20in%20<b>/home/content/85/7482585/html/balance/sitescan.php</b>%20on%20line%20<b>534</b><br%20/>/sitescan.php

I have tried deleting and reinstalling KC and SiteScan without any luck. Has anyone else run into this edge case?

It appears it was an issue with my server. Moved the site to another server and everything is working as it should.

I know this is a very old post, but I thought this might help someone:
I got the dreaded 'unknown error' from the KCfinder 'browse server' function.
Permissions were fine, but I tried 777 anyhow. No joy.
The problem was the Uploads folder maximum size limit of 100MB.
This may be specific to my hosting company, but it's worth considering.
I deleted a few large image files and bingo, end of problem..!
Hope this saves someone two or three hours of head-scratching!