On one of my PCs Win 10 is installed and I still use WLM 2011. However, after installing latest Windows update (KB3194496), all systems suddenly became extremely slow and I am unable to delete messages from my Inbox. If message in the list is unopened, clicking on the Delete button (red X) or on Delete key on the keyboard does nothing. If message is open, clicking on the Delete button (red X) closes it and opens the next message. The previous "deleted" message stays in the list unmoved...

What's going on? How to fix this problem and restore the Delete function?