Cannot upload ISO file's via webgiu

We are struggling to upload ISO files to one of our VM's (its in a 3-VM cluster)

When trying to do a ISO upload via the webGUI, we get the following error:

starting file import from: /var/tmp/pveupload-a646a885cc59e6485bf5b2102e3d9d6d
target node: vm04
target file: /var/lib/vz/template/iso/virtio-win-0.1.225.iso
file size is: 532060160
command: /usr/bin/scp -o BatchMode=yes -p -- /var/tmp/pveupload-a646a885cc59e6485bf5b2102e3d9d6d...

Read more