This property is not an actual count of bytes, but a count of the number of times the size of the file has exceeded 2^31. For example, the first time a file is written to, this property will be 0. If the Size property exceeds 2^31, the Size property will go back to 0 and the SizeHigh property will be incremented to 1. If Size exceeds 2^31 again, it is again reset to 0 and SizeHigh is incremented to 2. So, to find the actual file size, use:

(SizeHigh * 2147483648) + Size

DartStream Object  | DartStream Members