A call to EndUpdate must be preceded by a call to BeginUpdate, or desynchronization can occur. One way of making sure that both calls stay synchronized is to use a finally block:

try 
{
  i.BeginUpdate();
  // Do some modifications to the tar file
}
finally 
{
  i.EndUpdate();
}

In C#, the preferred way is to use the Xceed.FileSystem.AutoBatchUpdate class in a using statement.

This implementation of Tar is fully read/write compatible with the USTAR format. It is read compatible with GNU Tar archives whose entries do not use the header extensions of this format.

Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

TarArchive Class
TarArchive Members
Overload List