File upload and browse server not working for me

I'm running a new installation of YACS Version 8.3beta31.1. I cannot upload any images when using the text editors and cannot browse the server for existing images - get a 'page not found' error when trying to browse. I apologise if this has been addressed elsewhere, I did look, but can't find it. I think a recall a couple of years ago a similar issue with E107(same editors used, I think), which was a simple fix but I forget what it was. Anyone having the same problem? Please help this YACS noob