Copper piping that carries water, in a space that can go below freezing, is a bad situation just looking to get worse. Worse being the water eventually freezes and splits the pipe leading to a leak and ceiling damage.
If there are no viable other ways of running this line (in a heated space) to a drain I would suggest having the entire exposed line run in vinyl tubing or PEX tubing.
The other thing is a maintenance issue. If it took 12 years for this to happen I would strongly suggest you look at the end of the line where the water discharges. It's possible that bugs, bees or something else has plugged up the end of it. Small diameter piping/tubing that has a drop to it will auto-siphon once the condensate pump shuts down usually clearing any standing water out of the section of it that is in the attic. I'm suspecting something (the end being severely restricted) has stopped this process from happening. The other thing that can cause water to stand in the pipe would be a large build up of "crud" in the sump of the pump. Again a maintenance issue.
If you find bug or bees in the end of the pipe outside a simple paper clip slid into the end will most times make them loose interest.
Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.
The contractor who installed this line used copper because the vinyl tubing that had been used prior eventually wore through on the exit hole through the cinderblock exterior wall, fell into the attic, and ruined the ceiling below. The line runs almost straight up from the pump, then flat along about 15 feet of attic flooring, then *up* about 6 inches to the exit hole, then straight down to ground level.
I will check for bugs or other blockage as firecontrol suggested. I can also have a vinyl or PEX line run from the pump up to the top of the attic wall, then *down* to the copper pipe that exits the exterior wall, eliminating the 6" up-turn that might have trapped some water.
Thanks, everyone, for all the info and tips.