risa 0 Light Poster

MapFileAndCheckSum returns CHECKSUM_MAPVIEW_FAILURE(Could not map a view of the file) for file of size 758MB and above.For size upto 757MB it returns CHECKSUM_SUCCESS(normal behaviour).What is the meaning of this error?how to solve it?is there any file size limit to calculate checksum..............i want to calculate checksum upto 1.0GB/2.0GB