Assume ("edited files") you have you supplied him with a Project File and all the media?
You could try and EDL / XML for cross platform editing.
He could try only loading avis and then only mpegs to see if it is a file type issue.
What's edl and XML ?
How would I do that
I no longer have the laptop I edited the files on and I an s supplied him with all the files
It's so strange
Welll you wont be able to if you do not have the computer anymore.
Do a search on EDLs in Premiere (or any NLE) so you know about them for next time.
Whatever...I suspect the issue is at your colleagues end and needs to be sorted there. Someone with a Mac may chime in on how PPRO win project files and PPro Mac project files work.