In an AS2 transmission, delivery of the payload is guaranteed when the sender of the transmission generates a MIC (message integrity check) over the transmitted payload (usually as the message is signed), and when the trading partner returns a signed receipt for the transmission, the MIC that was calculated by the sender is compared to one returned in the receipt by the receiver. 

This is an error that comes from a mismatch between what MIC your partner reports receiving, and the MIC created by Arc when the transmission is sent. This could be an indication that the trading partner is calculating the MIC incorrectly; is you trading partner using an AS2 solution that has been certified as Drummond Interoperable?

You can find a list of Drummond certified AS2 solutions at https://www.drummondgroup.com/certified-products/b2b-interoperability/ and so long as your partner is using a Drummond certified solution, these kind of MIC mismatches shouldn’t be occurring. 

NOTE: If your partner is calculating the MIC incorrectly, this might be something that they need to bring up with their AS2 vendor would be needed to address this, but changing how you package the message might also change how they calculate the MIC. For example, enabling compression on the transmission if it is not enabled, or vice versa.