My ac,& furnace were both running fine until I switched it back from ac to heat it would not come on. The error code was blinking 10 times saying polarity and refer to twining its not working with another unit.

Make and model would sure help, but it could be a number of things from a loose wire to disconnected ground or a number of things really. Are you proficient with a multimeter?

Go to YouTube and enter reversed polarity twining and get some great videos on the subject.

https://www.youtube.com/watch?v=4Axj4WNRqMM

https://www.youtube.com/watch?v=iBtw6qpUBcQ

https://www.youtube.com/watch?v=FfIZ4_PcVu8

The twining refers to one thermostat controlling two (Identical/compatible) units.)

Basically you must check your wiring to find the fault best done with an ohmmeter, or a TECH!