Use a different browser: We recommend using Google Chrome, Mozilla Firefox, Opera, Safari or Edge. We still support Internet Explorer 11 and it works reasonably well, however we strongly encourage upgrading to Edge for a number of reasons - including security and technology incompatibilities.

Use Filemail Desktop! This is the most robust way of sending files - and it also supports sending folders. Grab it here: https://www.filemail.com/apps

Make sure the files you are sending are not opened in another program and that they are located on a local hard drive.

Be careful and do not remove or rename the files that are currently being uploaded. Doing so will break upload of removed or renamed files.

Try to send some other files - just to see if these are uploaded correctly.

Restart pc/mac and also router/firewall. You'd be amazed how many times this resolves the problem.