Hi,
Problems with j-link ... a recurrent topic, but ... I have recently uploaded to the J-Link Arm v4.76 from Segger and I could not either flash or debug from Keil. However, I could flash the device from the nRFgo Studio. The device was blank and I was trying to flash/debug the blinky project. I have downgrade back to the previous version v4.72 and everything is working fine. Could you have a go at this issue?
Btw, my OS is Windows 7. If any other info is needed just let me know.