The Fc.exe command does not work correctly in Windows Vista or in Windows Server 2008 when the command compares files that differ at every 128th byte of a character string
On a computer that is running Windows Vista or Windows Server 2008, you use the Fc.exe command to compare two files. If the two files both contain a character string that has more than 128 bytes, the Fc.exe command may not check the character at every multiple of 128. Therefore, when you use the Fc.exe command to compare the files that differ only at the 128th byte, the 256th byte, the 384th byte, and so on, the Fc.exe command will find no differences. This result is incorrect.
For example, assume that you have two files that contain a character string of 200 bytes. Also assume that only the character at the 128th byte differs from one file to the other. When you use the Fc.exe command to compare the two files, the command does not display the differences between the two files, and you receive the following output:
Comparing files FileName1 and FileName2
FC: no differences encountered
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB953931.