This document explains the slot error "Poll A Bus Parity / Poll B Bus Parity":
POLL A Bus PARITY and POLL B Bus PARITY
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These errors are counts of errors each card observes on the polling bus. The polling bus is a unidirectional bus from each Broadband Controller Card (BCC) to all the other cards in the shelf. It is a shared resource.
These errors indicate a problem with the BCC, backplane, or one of the cards sitting on the bus. If they occur on only one card, that card is most likely to have the problem. As the card will ignore the polling cycle that had a parity error, these errors can lead to Bad Grant errors, which result in cell losses.
Often, looking at the log to see what happened in the node at the time the errors began will point you to a recently-introduced piece of hardware or recently-activated card. The diagbus command may be used in some cases to guide you through isolation of the problem, but this is a very disruptive method because it brings the node down while it runs. Unless some other special information is present, cards must be removed one at a time until the errors stop incrementing. When this happens, you know that the last card removed was the culprit.