Can't make a mark

[ForensicArt]

I have been working on a painting and upon coming back to it now none of the tools will make a mark on the canvas. I can't draw, paint, erase or anything. Using a Wacom tablet, Mac OS in ArtRage 4. I have never had this happen before. If I open a new painting the tools work fine but not in the one I have been working on.
I have not intentionally changed any settings.

Any idea what is going on? Thanks for any help.

I could really use some help here. I have opened the painting now on a different computer, still a Mac, using a different Wacom and still I can't paint. I have a lot of work in this piece and can't find a reason for this behavior.

Is someonesane still around here?