Cannot read that as a ZipFile

Ionic.Zip.ZipException: Cannot read that as a ZipFile ---> Ionic.Zip.BadReadException:   Bad signature (0x55555555) at position  0x04541B3C
   at Ionic.Zip.ZipEntry.ReadHeader(ZipEntry ze, Encoding defaultEncoding)
   at Ionic.Zip.ZipEntry.ReadEntry(ZipContainer zc, Boolean first)
   at Ionic.Zip.ZipFile.ReadIntoInstance_Orig(ZipFile zf)
   at Ionic.Zip.ZipFile.ReadIntoInstance(ZipFile zf)
   --- End of inner exception stack trace ---
   at Ionic.Zip.ZipFile.ReadIntoInstance(ZipFile zf)
   at Ionic.Zip.ZipFile.Read(String fileName, TextWriter statusMessageWriter, Encoding encoding, EventHandler`1 readProgress)
   at SWPatcher.Patching.Patcher.AddZipToZip(String zipPath, String destinationZipPath, String directoryInDestination)
   at SWPatcher.Patching.Patcher.<>c__DisplayClassc.<Worker_DoWork>b__6(<>f__AnonymousType0`2 swFile)
   at System.Collections.Generic.List`1.ForEach(Action`1 action)
   at SWPatcher.Patching.Patcher.Worker_DoWork(Object sender, DoWorkEventArgs e)
   at System.ComponentModel.BackgroundWorker.OnDoWork(DoWorkEventArgs e)
   at System.ComponentModel.BackgroundWorker.WorkerThreadStart(Object argument)