Altera DE-1: "Error: Can't recognize silicone ID for device 1"

Dear fellow Forum Users,

I am struggling to flash a POF to my brand new DE-1. I can connect to the device via the control panel app, I can flash binaries to the memory from there, I can flash a SOF to the DE-1 via Quartus in JTAG mode, but whenever I try to switch to "Active Serial Programming" mode, and flash a POF, I get the message "Error: Can't recognize silicon ID for device 1".

I have followed the various threads on this topic, and have tried the solutions described in there, without success. What I have done by now:

- Try different USB cables and USB ports (both directly on the PCs motherboard, as well as via an active USB hub)

- Try different versions of Quartus (13 and 16.1), both with the same results

- Try different OS (Win 10 64bit, Win 7 32 bit via Virtualbox, native Linux Quartus on Ubuntu 16.04), all with the same results

The device is also autodetected when using the corresponding button in Quartus' programmer popup, however, I am greeted with the following popup when using it:

"Encounter devices with shared JTAG header for device 1. Please select your device: [] EP2C15 [] EP2C20"

(see screenshot at http://www.kersch.at/quartus.png )

I have not connected another FPGA or JTAG enabled device to this PC.

Any suggestions on how to proceed? Thanks for your support!

Martin