Error when verifying QSPI Flash

Hello - I am getting the message below intermittently during the verify of an FPGA (and spl at times) image.

The FPGA does not load so there may be another problem too but I was wondering if anyone has seen this and if so, resolved it?

Current hardware is: USB-Blaster [USB-1]

Found HPS at device 1

Double check JTAG chain

HPS Device IDCODE: 0x4BA00477

AHB Port is located at port 0

APB Port is located at port 1

Double check device identification ...

Boot Info: 3.0V QSPI Flash

Clock Select: 0

Start HPS Quad SPI flash programming ...

Initialize QSPI peripheral and flash controller ...

Assuming QSPI controller system clock is 50Mhz

QSPI controller baudrate setting: 32 (15)

Read Silicon ID of Quad SPI flash ...

Quad SPI Flash silicon ID is 0x1020BA20

Flash device matched

Manufacturer: MICRON

Device: QSPI_512

Assuming QSPI controller system clock is 50Mhz

QSPI controller baudrate setting: 2 (0)

Enable Four Byte Addressing ...

Verify Quad SPI flash ...

Progress [****????????????????] 22%

Error: Encounter invalid ACK status while accessing HPS

Error: Bulk read failure: Failed to read data in bulk

Error: Quartus Prime Programmer was unsuccessful. 0 errors, 0 warnings

Error: Peak virtual memory: 138 megabytes

Error: Processing ended: Thu Nov 17 20:27:36 2016

Error: Elapsed time: 00:26:49

Error: Total CPU time (on all processors): 00:01:09

Thanks

Kevin.