That was the first thing I tried. I've also tried disabling themes.
I am using the full set of Toolset plugins on a number of sites in quite complex ways. It only happens on sites on a particular server. Please look into whether there are any server settings that may cause this or if it's a known issue.
I have installed the latest version of types.
On one site I get this error:
Fatal error: Call to undefined function mb_strtolower() in /home/gridiron/public_html/wp-content/plugins/types/library/toolset/types/includes/classes/class.types.admin.page.php on line 744