I have installed PLECS Blockset and I am using a startup.m script to add the PLECS folder to the MATLAB search path. Now, whenever I start MATLAB R2013b it freezes during the initialization. If I uninstall PLECS or just remove the addpath commands from the startup.m script, MATLAB will start normally.
This problem is due to a bug in MATLAB R2013b. MATLAB freezes when opened if it executes a startup.m file that adds an info.xml file to the path. The PLECS folder contains such an info.xml file in order to register PLECS with the MATLAB Help Browser.
The recommended solution is to patch MATLAB R2103b as described in Bug Report 968648 (requires a MathWorks account).
If patching MATLAB is not possible, you can avoid the freeze by removing the info.xml file from the PLECS folder. However, you will need to remember to repeat this whenever you update the PLECS installation.