Unable to restore courses from old version of moodle to new.

Hi all,

We have recently set up a new moodle site running version 3.6.3. I have been tasked with transferring all of our old courses onto this new site.

I have attempted to do this using the backup and restore method, which allows me to get through to the last screen where you assign where the course is going to be (Restore as new course/restore into existing course) Upon clicking continue on this screen it produces the following:

Any ideas on what is happening? Thanks in advance.