When you get a Suspend/Reject email from CHEP it relates to dockets that have been exported to them but they cannot process. When you open the attachment on these emails you will see the reason. There are a number of different reasons and one of these reads "This movement number has already been submitted to CHEP and has been processed".
This can happen if a receiver declare account processes your transfer off a different account. To rectify this you should send a signed copy of your pallet transfer to the receiving account and ask them to authorise CHEP to correct it.
A recent example I came across is where the receiver declare account had CHEP process it as a Transfer Off their account instead of on to it.