I have faced an issue after turning on the Control system which was in shutdown for a long period.The Control system failed to restart showing error connecting to I/O pack <R>. On observation it was found that the < R>I/O pack of an Analog I/O card was not communicating with the switch. On replacing the I/O pack with a new one similar problem was observed on this new I/O pack. However, the I/O pack was operating perfectly on the <S> slot of the I/O card. So, the I/O board was replaced with a new one.
After installation of this new I/O card and packs we faced the same error of communication issue.
The problem was resolved after going into the card and selecting the modify option wherein the barcode number of the new card is to be selected from the available option in the dialog box.After then building and double downloading solved the issue.

 

Good news!

Yes; those barcode thingies can (and have) trip(ped) up many people.

I traveled to a site once where the technician had "memorized" the bar code from an I/O pack and kept typing it in and it just wouldn't connect (it was the only spare of that pack they had). This had been going on for at least a week, and it took me three days to travel to site. I asked him what the barcode was, and--much to his displeasure--entered it, and sure enough, it still wouldn't connect. I looked at the barcode on the pack and saw that two of the characters were reversed in the technician's memory. I had him enter the barcode as it appeared on the pack (from a cell-phone camera picture), and voilá! Problem solved. The plant manager was not pleased with him, or me when I submitted my report and time sheet for his signature.

 

Glad to know, you could figure it out and address it!
Since Mark VIe system doesn't have any back plane system there is no way to detect what is connect in the system ?
Hence you have to "Teach" the controller to look for a Terminal Bard with that bar code, so that it can provide an IP address and controller can communicate with it !