Probably something in your FTP upload didn't complete properly, or your FTP program converted the files to double-spacing and left extra blank lines at the end of the files thus creating syntax errors.
You can use the tool in step 2a of this FAQ to help find the exact error causing part of the page to be left blank: https://www.zen-cart.com/tutorials/index.php?article=82
You can also sort out one of the most common problems using this FAQ: https://www.zen-cart.com/tutorials/index.php?article=87
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