Description
If the Quartus® II programmer is being used to access an EPCQ256 device indirectly using JTAG and the Serial Flash Loader (SFL), only the enhanced mode Serial Flash Loader is supported, which is enabled by default.
If you have deselected the option "Use the enhanced mode Serial Flash Loader IP for the factory default helper image" in the Programmer Tools -> Options menu, attempts to access the device using this version of Serial Flash Loader will fail.
Resolution
In the Quartus II programmer make sure that the enhanced mode Serial Flash Loader IP is used. This is accessed using the Tools -> Options menu.