Cannot retrieve back up

For some reason everything has gone pear shape and I was asked to forward this
ICSharpCode.SharpZipLib.SharpZipBaseException: Encountered invalid codelength 0
at ICSharpCode.SharpZipLib.Zip.Compression.InflaterHuffmanTree.GetSymbol(StreamManipulator input)
at ICSharpCode.SharpZipLib.Zip.Compression.InflaterDynHeader.CreateStateMachine()+MoveNext()
at ICSharpCode.SharpZipLib.Zip.Compression.InflaterDynHeader.AttemptRead()
at ICSharpCode.SharpZipLib.Zip.Compression.Inflater.Decode()
at ICSharpCode.SharpZipLib.Zip.Compression.Inflater.Inflate(Byte[] buffer, Int32 offset, Int32 count)
at ICSharpCode.SharpZipLib.Zip.Compression.Streams.InflaterInputStream.Read(Byte[] buffer, Int32 offset, Int32 count)
at ICSharpCode.SharpZipLib.Zip.ZipInputStream.BodyRead(Byte[] buffer, Int32 offset, Int32 count)
at ICSharpCode.SharpZipLib.Zip.ZipInputStream.Read(Byte[] buffer, Int32 offset, Int32 count)
at ICSharpCode.SharpZipLib.Core.StreamUtils.Copy(Stream source, Stream destination, Byte[] buffer, ProgressHandler progressHandler, TimeSpan updateInterval, Object sender, String name, Int64 fixedTarget)
at MailClient.DbBackup.FormBackup.Restore(String backupFile, CancellationToken cancellationToken)
at MailClient.DbBackup.FormBackup.Restore(CancellationToken cancellationToken)
at MailClient.DbBackup.FormBackup.<>c__DisplayClass28_0.<MainForm_Load>b__0(Object a, DoWorkEventArgs b)
at System.ComponentModel.BackgroundWorker.OnDoWork(DoWorkEventArgs e)
at System.ComponentModel.BackgroundWorker.WorkerThreadStart(Object argument)
Hope someone can make sense of it. Thanks.