Paul Collins
I'm assuming this is oil based paint. Almost certainly due to lack of stirring of one of the new environmentally friendly reduced VOC content paints. These need A LOT of stirring before use and can be very slow drying. I would also add at least some white spirit despite instructions not to on the tin. If it's drying at all, ie. becoming tacky, it will dry eventually, maybe after a week or so. If it isn't, get a white spirit soaked rag and remove as much as possible and then allow to dry. Kind regards Paul Collins