I cannot export a decision plan after my first attempt to export it was interrupted.
You would see an error message saying that the Classification Server cannot work the same file because it is being used.
This situation can happen if the computer crashes or the network is disconnected while the sarc file transfer is taking place.
Resolving the problem
Manually delete the temporary sarc file on the server.
It can be found here: [Content Classification install folder]\Data\rw_[kb name]\[kb_name].sarc.tmp