Hi
Use cmd line and install from here;
If there are errors follow the instructions in the wiki.
This occurs almost every time.
https://www.open-emr.org/wiki/index.php/OpenEMR_4.1.2_Ubuntu-Debian_Package_Installation
Then follow the steps I posted in the forum.
Make sure version and patch is the same as your currently using before to restore.
Once you have 4.2 upgrade, then you should be able to do a cmd line openemr upgrade. The problem your encountering is due to the php change that occurred at that time.
Hope this helps,
Henry