Only user number 1 can add content Recently all users (except UID 1) lost the ability to add content.

When going to node/add we get the message "no content types created yet"

When going to node/add/page we get "Access Denied, you are not authorized to access this page"

There are people having similar issues like here - https://www.drupal.org/node/1073994

I have already checked the navigation menu to see if that was the issue, since it seems to be a known bug, but this was not the case. All the permissions are set correctly in the permissions UI and database too.

I am not sure if this is relevant, but the site was migrated from 6 to 7

Any insights would be appreciated!
This is indeed most likely an access issue. However, I don't think it's something with Apache Solr but more with some of the additional modules you might have enabled. Can you list them with the versions here?

Also, as mentioned above, disable apachesolr access and rebuild your permissions. Check if it is still the case?