Not same model as you, had mine for yrs, similar problem, I find on mine I need to hold it in slightly/for a short period of time, give it chance to scan it probably. After that ok, until the next time, same thing again, slightly annoying, but I am used to doing it now, so does not bother me anymore, Reason why, ??? Possibly some software bug, not quite checking in correct order. But try just holding it closed for a short time, you will feel when it is ok, It sort of stops reacting, you do not need very much pressure, other wise you could damage it. I assume you intend to use it tomorrow, so impossible to get it to a repair place, But for the cost of repair, is it worth it if above works. Merry Xmas
SD, December 2011