Error message "Invalid JTAG configuration" with SignalTap

[Altera_Forum]

I am using Quartus 10.1 on Win7. Configurating my Cyclone 3 FPGA with USB-Blaster works fine (downloading sof-file via SignalTap "SOF Manager" Button). 

But it is not possible to comunicate with the FPGA via SignalTap ("Run Analasis"-Button) due to this error upcoming error: "JTAG communication error". Before pressing this button, the message "Invalid JTAG configuration" is shown.   What went wrong ? I can download my sof-file into the FPGA via JTAG, but I cannot communicate with the device !   Yes, I did a recompilation with the settings in SignalTap.   Thanks in advance.

[Altera_Forum]

do you have another instance of quartus open or did you still have the programmer module you used to upload the sof file? i've found been getting this error when this happens. Probably port contention between the different instances trying to access the usb-blaster port.

[hyoun5]

 i've found been getting this error when this happens. Probably port contention between the different instances trying to access the usb-blaster port. <-

How do I fix this?

I need your help.

​Thank You​

[Altera_Forum]

No, just one instance is open. 

But I have found out, that this happens when the qsf-file is set as read-only (version management used). Setting the file to writeable solves this problem. But unfortunately no hint is given by quartus.   Thanks for replaying. Works fine now.