WinSCP IDisposable Wrapper
a condition to be met like if (someBoolean == true) can be simplified to if (someBoolean). For reverse check use the Not operator ! like if (!someBoolean).  
Dipsose() should not only call Close() but also get rid of session, sessionOptions and transferOptions by calling Dispose() if they implement IDisposible or at least setting them to null.  
SendFile()  

you should declare the variable as near as possible to its usage and instead of catching .. rethrowing the exception, let it bubble up the tree. So it can be simplified to    

public TransferOperationResult SendFile(string SourceFile, string DestFile)
{
    return session.PutFiles(SourceFile, DestFile, false, transferOptions);
}

if comments don't add any value, like explaining why something is done (what is done should be explained by the code itself), they should be removed like  

//public properties