This has the implication that the Size attribute can only contain the value of a signed 32-bit integer (2147483648) which is equal to (you've guessed it) 2 GiB. I.e., any file contained in a file list that is above 2 GiB is going to be considered invalid by the schema.<xs:attribute name="Size" type="xs:int"></xs:attribute>
The proper value should be the use of an unsigned long:
<xs:attribute name="Size" type="xs:unsignedLong"></xs:attribute>