FATAL ERROR K2 HELPERS ROUTE.PHP

I was trying the templates, and i had no problems.
I was trying TWN2, installed as usual, and, when i try to go to the home (www.bajaboo.com), i receive this message

Fatal error: Call to undefined function mb_internal_encoding() in /home/baja/public_html/components/com_k2/helpers/route.php on line 59

i'm using joomla 2.5.4, and i have the problem with all the browser..

I thought it was a server problem, but i have other "testsites" on this server and they work properly with other templates..

What should i do?
thanks in advance!

Hi

First of all please try update K2 to the latest version. If this will not fix it You should report it on K2 forum.

I've found that this function needs to be enabled to work, but if You are telling that's not a problem on other pages than it shouldn;t be a case. But I advice to check it anyway: http://www.php.net/manual/en/mbstring.installation.php