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if (!File.Exists(this.SaveFile))
{
    File.Create(this.SaveFile);
}                    

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        public void BackupFile(String file)
        {
            ZipInputStream ZipStream = new ZipInputStream(File.OpenRead(this.SaveFile));
            ZipEntry theEntry;
            FileInfo fileinfo = new FileInfo(this.SaveFile);
            if (fileinfo.Length > 0)
            {
                while ((theEntry = ZipStream.GetNextEntry()) != null)
                {
                    if (theEntry.IsFile)
                    {
                        if (theEntry.Name == file)
                        {
                            FileInfo fi = new FileInfo(this.TempDir + file);
                            if (theEntry.DateTime == fi.LastWriteTime && theEntry.Size == fi.Length)
                            {
                                //Datei existiert, abbrechen
                                ZipStream.Close();
                                return;
                            }
                        }
                    }
                }
            }
            ZipStream.Close();

            /* Datei Zippen */
            ZipFile zip = new ZipFile(this.SaveFile);       //Hier kommt die Exception
            zip.BeginUpdate();
            zip.Add(this.TempDir + file,file);
            zip.CommitUpdate();
            zip.Close();
        }                    

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byte[] emptyzip = new byte[]{80,75,5,6,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
FileStream fs = File.Create(this.SaveFile);
fs.Write(emptyzip, 0, emptyzip.Length);
fs.Flush();
fs.Close();
fs = null;                    

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ZipFile zip_del = new ZipFile(this.SaveFile);
zip_del.BeginUpdate();
zip_del.Delete(file);
zip_del.CommitUpdate();
zip_del.Close();