When u r logged in as a guest or registered user and when u click on download button and

-If u get access key is expired here's the possible solution.

Firstly raise the link expire time. Next if it is raised and even if u get access key is expired request a new one from admin panel

Go to host packages > list package > Guest edit allow direct download > select yes

And save it and download a file from guest package and then again go to host packages and disable the option allow direct download.

Now you will see that download works and access key is expired problem is fixed.

If u host a file on remote server and getting this error run yoursite.com/syntimer.php

That will fix the problems

Hope this helps