A Microsoft Reserved Partition, or MSR, is a partition of a data storage device, which is created simply to reserve a chunk of disk space for possible subsequent use by the operating system software of a Windows operating system (Installed to a separate partition). It should be noted that no meaningful data is stored within the MSR; though from the MSR, chunks may be taken for the creation of new partitions, which themselves may contain data structures.
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Excluding the MSR from the backup should solve the problem.