Can the upload to the same directory if they do it through the file manger page? If the problem is just on the publish page, open your developer tools and look at the console- any javascript errors? If so, it might be this issue: https://github.com/ExpressionEngine/ExpressionEngine/pull/447
The other problem I can think of happens if you’re using MSM and have the same file field on 2 different sites- you just can’t do that.
Packet Tide owns and develops ExpressionEngine. © Packet Tide, All Rights Reserved.