I was plagued with this issue as well. Loading the dll error dialog would take several minutes whenever opening a scene or just importing via forest pack or merging. It seems a file becomes corrupted in the ENU folder and it needs to be reset.
Best solution I've found is:
Firstly, In 3dsMax, go to Customize > Customize User Interface. Save any workspace configurations you may have such as toolbar setups and quad menus.
Close 3dsMax
1. Go to this folder C:\Users\User\AppData\Local\Autodesk\3dsMax\xxxx - 64bit\ENU
2. Create a copy of your 3dsMax.ini file
3. Then delete the entire ENU folder
4. Launch 3dsMax and a new ENU folder will be created. It will load as if launching for the first time.
5. Close 3dsMax
6. Replace the new 3dsMax.ini file (newly created in the new ENU folder) and replace it with your old copied version. This will have your hotkeys, user configuration, path config etc.
7. Launch 3dsMax
8. Open your Customize User Interface dialog and load the previously saved workspace files.
This will prevent any MrMaterial Dll errors from popping up and will still retain your previous workspace and hotkeys so you don't have to set it all up again. The ENU files may become corrupted again in the future, in which case you'll have to redo the above method. Honestly though, it's better to do this than sit there waiting for it to cycle through every materiall dll error every time you open a new file.
Best of luck!