Having just executed BackgroundNeutralization on an image, I attempted to execute it a second time, however I had the Statistics tool open (with the Tick mark set) and Statistics was still in the process of automatically recalculating stats following the first run of BN as the image had been modified.
The result was a popup Error window, with the message "The view is locked for read/write operations: Image416".
However, I am unable to clear the error window, moving the mouse into the error window turns the pointer to the 'busy circle' and the OK button cannot be clicked. The red window close X button can be clicked but has no effect. I've tried Tab/Space, Esc, Enter and so forth but the application appears deadlocked. No other elements of the PixInsight UI are active/responsive, though the error window can be moved.
If relevant, the grey progress window from Statistics is still visible (in fact permanently visible even switching to other applications) and reports that Statistics was computing the MAD property at the time.
The only resolution was to kill PixInsight with the Task Manager.
Screenshot attached.
Win7 x64, PixInsight PI-windows-x86_64-01.08.04.1195-20151218
I'll be more careful in future, but hopefully this report helps.
Richard