Wow, this error caused me some grief for a couple of days. Anytime that I would access the “Configuration"menu of my Drupal 7 site I would get the error, “One or more problems were detected with your Drupal installation. Check the status report for more information.”
Every time that I would check the status report page, everything was green with no errors. I also checked the logs and no errors were reported there. After spending a few hours messing with modules and reloading different versions of my database, and questioning my Google-Fu, I decided to disable the “Update Manager” module and re-enable it. Ah ha, this gave me the clue that I needed.
After finally deciding that the Drupal “Update Manager” module may have an issue, I encountered an error when trying to re-enable it. The error was, “The website encountered an unexpected error. Please try again later.” Since I was working in a non-production environment, I also have error messages enabled and this error was produced:
DatabaseSchemaObjectExistsException: Table _cache_update_ already exists. in DatabaseSchema->createTable() (line 657 of includes/database/schema.inc).
Terrific! Well, I messed around with truncating the table and running update, but those actions did not work. So with this additional information, I went back to Googling. Then, I found this post on the drupal.org website.
Buried within was the answer. The resolution to this problem was to reset the schema_version for the update manager module (modules/update/update.module) in the system table to a value of 7000. The value in my Drupal database was ‘-1’. Here is the SQL update command that I used to change this value (I use MySQL for the Drupal database):
update system set schema_version=7000 where filename='modules/update/update.module';
After changing the schema_version value in the database, the only step left is to just run a Drupal update (/update.php).
Finally, I am free from this issue. I hope that this blog post will save some others from the same frustration.