Hi Abid,
For your queries, the problem could be that you are running v4.3 with PHP7. We only upgraded to PHP7 support with the latest (4.6) release:
https://github.com/subjectsplus/SubjectsPlus/releases. I would suggest you try upgrading to that and see if your problem is resolved. You will, of course, have to make any changes to the public interface again.
As for adding a publisher field, that is certainly possible, but you would need to add a new field to the database and modify a few files. It would be easy to break something. The new version of SP--which is a complete rewrite, and not really close to done--should allow you to add custom fields, but in the meantime, could you do something hacky like adding the publisher information to the display notes field?
That wouldn't look great, it would be like
Database Name
Note: Publisher: Wiley
and then just start storing the publisher data in the Display Note field. Not sure I would recommend this, but it could work.
Andrew