I ran into the same issue using Ampps, and it's a pretty easy fix. The trouble comes from Ampps being so easy to use, you never think you'll have to adjust very much within it. Come to find out, sometimes you do.
When you create your FTP accounts within Ampps, you'll need to play close attention to what directory you are giving the account access too. By default it's usually not the right directory that is listed. For example, sometimes in the directory box you will find this - Ampps/www/admin. You don't want that. You need to grant access to your oxwall install directory. Other times you may look in that box and see that it instead says Ampps/www/. This may or may not be correct either. If you go to your website by simply typing in "localhost" in the address bar, then this is okay, and should work. BUT... since "by default" ampps is going to install Oxwall into a folder name "oxwall", that is what the directory of your FTP account should be pointed to. So in that directory input field for the FTP account that you create, "make sure" that it says C:/Program Files (x86)/Ampps/www/oxwall
I am going to guess that this is the trouble everyone is having, and will fix the problem.