this does work for me if the files to compress are big enough to produce several volumes:
SevenZipCompressor szComp = new SevenZipCompressor(true);
szComp.VolumeSize = 1024 * 1000 * 10;
szComp.CompressionMethod = CompressionMethod.Lzma;
szComp.CompressionMode = CompressionMode.Create;
szComp.CompressionLevel = CompressionLevel.High; //Ultra throws Exception...
szComp.ArchiveFormat = OutArchiveFormat.SevenZip;
szComp.PreserveDirectoryRoot = false;
But if the resulting compressed file is smaller than VolumeSize, just a file "name.7z.001" with size of 32 bytes is created. Opening this file shows "name.7z" in the file list, but this file can not be extracted.
When removing the "szComp.VolumeSize = 1024 * 1000 * 10;" line completely it produces a single compressed 7z file without problems.