Why I'm getting 'Cannot redeclare drupal_error_levels()' error?

Question

I have one site running Drupal 7 on server and I get the following errors for the specific page and on specific action like (clearing cache, or page like '/calendar') otherwise site is running fine.

Fatal error: Cannot redeclare drupal_error_levels() in includes/errors.inc on line 16
Fatal error: Cannot redeclare class QueryConditionInterface in includes/database/query.inc on line 16

I am getting this errors on production server. If I run same code and database on my local server or any other server of Host provider it runs fine without errors.

I don't know what causing this errors I have checked files also and there are no duplicate files.

Answer 1

This is probably too late to help the OP, but I experienced these same errors (on some pages/URLs, but not others) after moving my Drupal/CiviCRM site to a new server at the same host. I had some symlinks that were created to work around a CiviCRM problem, and they were broken after moving the site. Correcting those symlinks resolved this for me.

I had further issues, but I don't know if they were related. If this doesn't completely resolve your problem, let me know.

Answer 2

I was able to specify this problem in my installation. I modified a module and template. For that I made a copy of the specific module/template folder as backup. What Drupal obviously does is to check for folders in those two folders and load them - whether nessecary or not. And of yourse now I have twice all the functions and css-classes loaded :-Q This doesn't happen right away but as soon as you go to modules or templates in the drupal backend ;-)

Answer 3

This error is commonly caused by PHP caching and optimisation engines.

So please disable extensions such as XCache, eAccelerator, XDebug, etc., restart memcached if having and the error should be gone.

If it's still happening, check your database collation (it should be case insensitive, e.g.: general_ci).