I've seen this come up during autosave or other functions, and the dialog window in those cases reports what command is running.  Often, I'll see the CPU/Memory values making sense, corresponding with "something" happening.

My issue is with unspecified commands (i.e. "SOLIDWORKS is busy running a command" without any indication as to what command is running) that show 0% CPU without any indication that something active is going on.  Program Manager shows SW as "Not Responding", also shows 0% CPU.  Memory is in the order of a 

For the current instance of this behavior, I'm looking at one part (multiple bodies, a few equations, moderate complexity), have a number of other parts and assemblies open in separate windows.  I had called up other applications and when I came back to SW, it responded with the "busy" dialog - I hadn't previously started any other commands (e.g. save or rebuild).

Additionally, with the "busy" dialog open, I can't even minimize the SW window to view the desktop behind it - I can cancel the dialog, returning to the "white glaze" (?) frozen window, but if I try to minimize the window, the "busy" dialog comes back.  I can't even use the windows manager to minimize all windows at the moment.

I've now quit out of solidworks, at least the autosave is working moderately well at the moment...