After installing K2 one of the first things you need to do is creating at least one category.
But after saving this category it results in a blank page.
With a search in this forum, there is this issue and solution:

"You have to enable the Multibyte String extension on your PHP server."

Well: Multibyte String is enabled and still we have this problem.

Is there anyone that has another suggestion?

If you Set Joomla Debug on and under the servertab turn error reporting to highest it should return an error rather than a blank page. This will hopefully give you an idea of whats going on

This is the result:

Fatal error: Call to undefined function mb_regex_encoding() in /data2/sites/xxx/administrator/components/com_k2/tables/k2category.php on line 50