I am using Joomla 1.7 and K2 2.5.4 and when I try to create a category and click save it loads a white page and never creates the category.

I used an older version with Joomla 1.5 a while back on the same server and it worked.

I have been reading and read something about mbstring. If this is "Multibyte string support" that is listed under the Information tab then it is enabled.