If you're using FAT32 formatted boot media, SmartDeploy can split your image WIM file into smaller parts to fit within the file size restriction of FAT32 (4 GB) when it creates offline deployment media. However, SmartDeploy cannot split individual files within an image.
If you're trying to do this and receive this error, a file on your Reference VM may be larger than 4 GB.
WinDirStat is a free tool that is helpful in identifying files and folders that are taking up space on your disk. Use this tool to determine if there is a file that is larger than 4 GB.