"Output Microsoft HTML Help contains an absolute path for publishing. Change to a relative path..."

I suddenly get the error message

"Output Microsoft HTML Help contains an absolute path for publishing. Change to a relative path to continue."

when I try to generate a .chm file from FramaMaker 19.

It did work just a week ago, but not today - and I have made just one minor text edit since.

Is it the output folder I'm suddenly is supposed to change? Or something else?

(I can still publish the same document as pdf.)