Magento – Mage registry key already exists Error

errorkeymagento-1.9registry

I keep getting an error stating
" There has been an error processing your request
Mage registry key "em_current_theme" already exists

Then a bunch of Trace: numbers"

It happens on the mobile version of my site and i'm wondering if there is a quick fix to resolve this issue once and for all.

It's most likely caoused by some extension you have installed.

Try to disable the new extension you installed and disable the compiler. Then re-compile again.

You can do this from the admin panel or if it's not accessible try those commands:

php -f shell/compiler.php disable
php -f shell/compiler.php clear
php -f shell/compiler.php compile

You can also diable the module in app\etc\modules directory.

This error arriving due to empty values in registry.

to prevent it, you need to disable 'compilation' mode, and if you want to use it, re run it.

php -f shell/compiler.php disable
php -f shell/compiler.php clear
php -f shell/compiler.php compile

I got the Solution of this issue:

This issue occur when your core_config_data table is corrupted.

Please follow the below to fix this issue:-

Go to your phpmyadmin
browse the core_config_data table and check there is some same value stored in config_id column and this field is not set as an auto increment.
First change the same value and make them unique. because this field is auto increment and stored unique value.
Go to the structure of the table and set the config_id as primary.
After that set config_id field auto increment.

Now check your Issue that may be fixed.