Ok to lower the urgency, use your backup to use the slightly older version of joomgallery.
If you did not create a backup, sounds like you didn't listen to what it says on the frontpage:
as always recommended at this point - please backup your file system and the database content.
Always read the fine print, especially when it's on the frontpage.
But this does sound like something that could be addressed. If I was you, I would create a fresh installation of joomla, install joomgallery, and see if these errors occur. (for me installing joomla takes seconds because I have a cpanel, not sure how it is for you). This test I mentioned will establish if it's related to your server or your extensions installed on your site.