Other causes for MOUSE "Initiating Simulation Launcher" status bar freeze?

I'm seeing the MOUSE engine (MOUSE Simulation Launcher) lockup during it's startup phase without an error message. It occurs when the status bar text is "Initiating Simulation Launcher". One time I saw this error before on Mike Urban 2012, I eventually traced it to weir and a valve element with the same MUID and changing one MUID fixed it.

Anyone else seen other causes? That's not the issue this time, so I'm trying to debug why I'm getting the error.

Might not be relevant because my Status bar message was different but...it happened to me during an LTSimulation while "Loading Boundary Conditions". No error message. The Problem was in the rain boundary conditions (in runoff bc).

Actually, I ended up tracing it to a boundary issue as well. I'd erroneously left a head boundary as an external timeseries (DFS0) instead of a gradual fill (on a cold start). I guess the significant jump in head was too extreme. (I was overriding the max pressure in dhiapp.ini, so that probably would trigger an error at least in normal model runs)