There has been an error processing your request admin panel in magento

step 1  main directory in tmp folder create
step 2  tmp folder Set directory permissions to 777 or 755
step 3 Open “lib/Zend/Cache/Backend/File.php“
step 4 locate the following code

protected $_options = array( ‘cache_dir’ => null

and replace with

protected $_options = array( ‘cache_dir’ => ‘tmp’