Why won't my 2009 Mini Hard Top shift in cold weather?

Ever since Christmas Eve, the car won't shift without excessive force.  I leave the car in
reverse when I park, and in the morning, it's almost impossible to get to neutral, then into
first, etc.  After a bit, I run it through the gears and it loosens up and shifts without a
problem.  I assume it is related to the cold, but it's been in the same climate for five years
without a problem.  Anyone know what could cause this?  Can it be fixed?  Am I doing
damage to the car by forcing it into gear?  The clutch seems fine.