Two things...try the previous version of TWRP. I believe there were other threads mentioning issues on the Maxx with 2.7. Second, I got the exact same issue trying to downgrade. I just wound up using RSD lite to flash the 4.2.2 FXZ and it worked fine after deleting some lines from the XML file. Basically if I got an error flashing, I deleted that line from the XML file, and continued that process one by one until the file successfully flashed.

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