Error in Module 'timezonedb' already loaded

Hi everyone,
I use Codeigniter [b][b]3.1 to programmer a website, it's perfect framework for php.[/b][/b]
[b][b]recently i show error in bottom page said : [/b][/b]

Code:

A PHP Error was encountered

Severity: Core Warning

Message: Module 'timezonedb' already loaded

Filename: Unknown

Line Number: 0

Backtrace:

i search for module timezonedb in php.ini and in .htaccess files i don't find any duplication for loading this module.
could someone help me to fix this error.

thanks