[New York]

it will sound strange,

1) but search your x-cart 5 directory for any fieles with tpl0000644, php0000644, png0000644.

x-cart use 7-zip to compress, if you uncompressed on SOME files it end up with those extensions.

2) if you disable some default module upgrade may fail


3) if you upgrade from 5 you better just reinstall clean 5.1.3.

If above not help let me know i have more to share...

Good luck