Tag Cloud error

I have exported my wordpress xml file because i changed my host and i’ve used the wizzard to convert categories into tags. I activated the Tag Cloud sidebar widget and it shows up just nice.
The issue is that when i try to click on a tag it gives me this error page:

Archive for the tag:
Fatal error: Call to undefined function UTW_ShowCurrentTagSet() in bla-bla-bla\wp-content\themes\theme_name\tag.php on line 7

In tag.php on line 7 i have this code:
<h3>Archive for the tag: <?php UTW_ShowCurrentTagSet(‘tagsetcommalist’) ?></h3>

How can i correct this issue ? Thanks in advance.