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.