This is a known issue that is partially fixed.
If you run a DI Update, you will have a new file /user/bin/gopigo which used to be named /user/bin/gpg in conflict with the Gnu Privacy Guard gpg
Dexter had this gopigo-related gpg for a while, and people never ran into issues, and now you're the third one in about a week. Something outside of Dexter has changed, potentially at the Raspberry Pi Foundation?
Would you mind sharing what exactly you're doing, so investigation can be made?
In the meantime, feel free to copy over the gpg file found in a regular Jessie installation. It will not hurt the robot.