Dave - I haven't seen  the "An error has occurred in the Script on this page" again since cycling the Hide script error check box a few times and restating DXKeeper and Pathfinder. But is reference to the issue of:
Seeing the error  of --- a small window popping up saying === A call sign not found even though the lookup info is entered in the Capture window and shows in the Pathfinder window"

and you asked

+ What's an example of a callsign that produces the above behavior?
a couple  that this happened on  are JH1RGG, K5DX, K5LG, NA5DX, K5PXP

73 & tnx
Paul w2eck