So, I'm still upgrading these KRC2s (KSS 5.5.15, SafeOp 2.1). And everything seemed to be going fine until I tried my first Mastering Reference.
The program ran fine, I could see the indicators for the MasRef sensor (on the sensor itself, and in the SafeOp Diagnostic screen) go false as the robot hit the reference position. The robot pulled away, hit the end of the MasRefReq.SRC program... and threw a fault message (with no number) that says "Mastering reference failed; system variable $MasteringTest_InPro is FALSE".
This system variable, and this message, are not mentioned anywhere in the SafeOp 2.1 manual. It's also not declared in any of the .DAT files in the robot.
My reference position is taught in both the MasRefStart program and in the SafeOp setup screen.
The one odd thing about this robot is that is has 9 axes, but only 8 of them show up in the SafeOp config screen -- the E3 axis is a dual-servo axis that's part of the end effector and doesn't need SafeOp monitoring. E2 is a single-servo part of the end effector which, likewise, does not require SafeOp monitoring, and is crossed out in the Monitoring Axis section of the SafeOp config screen. E1 is a kinematically integrated KL1500 rail, and is "active" in the SafeOp "Monitored Axes" menu.