SLC 504 Download failed, Communication Errors!

As part of an upgrade I am working with 7 different SLC programs. I had the first program in a test controller in my office running and communications all healthy. I went to download the second program which has all the same processor and comms configurations and got "Download failed, Communication Errors" once it got to the "writing executable files" part of the process. After messing with trying to get that to work for a bit, I went back to the first program and got the same error with that program, even though it had been fine. I've been on the knowledge base and have tried deleting harmony files and updating rslinx as suggested by them. I can download a blank project to the controller and go online without any trouble.

At a total loss as to what the problem is and hoping someone here might know.
Thanks

Welcome to the PLCTalk Forum community !

What communication driver are you using ? Any chance there's a real communication error occurring, like with a loose wire or missing termination resistor ?

Hi Ken,
I'm going through the backplane of an L7 and out of a DH+ card. I can download and go online with a blank project so pretty sure that the wiring is all ok.
Thanks

check hardware configuration mismatch

Why not connect directly to the SLC5/04 ?

I don't think that downloading a small program rules out noise or other organic communication errors, because the probability of a checksum error goes up with the size of the data packets. A default program with no routines might get through where an ordinary application program won't.

But passing through a ControlLogix backplane and a 1756-DHRIO also raises the possibility of data mis-handling there. In particulary I remember a bug where just one confirmation code wouldn't be processed by the DHRIO so the "write to EEPROM" function on an SLC-5/04 would appear to fail. Obviously this isn't the same function, but maybe there's something similar with a data block size limit, or a buffer availability error for a large download.

If you can, connect directly to the SLC-5/04 via DH+ or DF1 and try your download that way.

Hi, thank you. I've been out of the office so only read replies this morning. I will try connecting directly and see how that goes. The reason for going through the L7 is because of replicating what the customer has on site. It's just strange that the one program I did download before this error occurred also won't download now.