A bug was discovered in the MDD Multi-Loader after 11.5.1 had shipped, that caused scenes with NULLs to lock up Layout, apologies for that.

Attached is a hotfix.

Download this file and replace the 'MDD_Multi-Loader.lsc' file in "YOUR_LW_INSTALL\support\plugins\input-output\".

MDD_Multi-Loader.zip