Appears to be a bad patch from Microsoft.

KB3114409 dated December 08 2015 has caused many users to only be able to launch Outlook in Safe Mode.

If you need to roll back, I wrote this recently on ‘Rolling back from a bad KB Update‘

Feel free to comment on your experience with this KB, I’ll update this post with any other information I find.

I also found this forum thread on Windows TenForums about the issue.

Update 10th December 2015:

Thanks for all the comments – glad it’s helped you all out. We’ll see if the patch gets reissued. Rehash of some of the details below:

Webmaster advises: This is being sold as an improvement: “Adds administrative support to prevent Outlook 2010 from booting into safe mode. Administrators set this function in some scenarios when they have add-ins that must be enabled.”

This technet article contains the key you can modify to stop Outlook going into Safe mode.

Alexej Kucher advises that: On a 64 bit machine with 32 Bit Outlook you have to create following registry key:
HKLM\Software\Wow6432Node\Microsoft\Office\14.0\Outlook\Security\ DWORD: DisableSafeMode = 1

Wayne DeJulia advises that the command to uninstall is: msiexec /package {90140000-0011-0000-0000-0000000FF1CE} MSIPATCHREMOVE={14CDCBF7-3CCC-42E2-A5BB-2D4926E16FAA} /qn /norestart

boozydaboozer  advises: Looks like Microsoft has removed KB3114409 from Windows Update.

Update 6th Jan 2016
I’ve noticed clients keep getting prompted to uninstall this, so once your desktops are all unpatched, you will have to decline the update.