Error even though clean install

Hi!

I cannot use my search function, getting this Error message:

Fatal error: Call to undefined function mb_strtolower() in /home/picazoo/public_html/catalog/model/catalog/product.php on line 399

I have also changed database, but not the user.
Also i cannot put in options, or related products. Nothing PopUp when i typing in the forms.

I have no domain name so i conect to the FTP via IPnumber and local enviroment - i have changed host file in widows.

I dont know what to do, I thougt it was my custom theme but even after a clean install and a new database it is not working?

Thanks,
Henrik

Version 1.5.1
Theme: Shoppica

ask your host to add the mb extension. its something i fixed but seems to have returned because of google code not replacing files. you might also want to try the svn version if you know how to download it.

Than you Daniel!

I contacted my Host and asked them to do this change for me. Then the search box worked!