if ((data[1+6] == 0x83) & (data[2+6] == 0x01)): exception in read holding reg

[pandya2368]

I am facing the issue in Holding Register from PLC. I am sending 5 register value from PLC with increment in every 7 second. I am pressing the Read Holsing register button every 5 second to check weather value changed or not. code works fine but sometimes its gives exception of Index out of range. and if i press Read holding Register button again its started working again.now, i use one sofware (which works like PLC) so with this software code working good there is no error in working with software. I checked one software with PLC to see what data coming from PLC so i can be clear that PLC is working well or not. but PLC responding in every 7 second continues. so what am i suppose to do now?! You can see in image. I run the code on Raspberry Pi 3 and Windows 10 but facing same issue.