Zipped ROM from Sammobile not flashing

I need to flash a stock ROM on my original Note, so I downloaded a stock ROM zip file from Sammobile and stored it on my internal memory. The current ROM on my Note is the Union ROM LT4, with the latest Speedmod kernel. I went into recovery, wiped data and did factory reset, and then tried to flash the new stock ROM by selecting the zip file, but the flashing fails. I'm not sure why this is happening. Am I missing something?

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