Airflow is critical for the safe operation of the furnace, especially in places where there are bugs, mice etc. They get into the furnaces and cause all kinds of problems.
As stated by Kevin & Lipster, look for blocks in the intake and exhaust. The block (may not be visible and internal to the furnace. Mud Daubers and wasps can get deep inside.
If its not that, then likely its a problem with airflow on the blower side. If you look up "Sail Switch" there's all kinds of information online. Its a very common 'failure' or point that detects something else that is wrong. Be careful with propane --- if you have a leak, this is the kind of thing .... well, you just don't want to have leaks.
I'd call the factory on Monday and get guidance from Cary.
