Flashing the Synergy S7


I am using a Renesas Synergy S7. I want to flash it using a self-written program. During the transmission of individual 1000-byte blocks, interruptions occur at random points. I transmit the block, but no longer receive an acknowledge from the S7 processor. What could be causing this? Is it possible to read an error code? Can I simply retry transmitting the block?"

Thank you.