yes. actually its 5 files. thanks for the reply.
I've already resolved this issue by changing the last boolean parameter of ShapeFile() function into FALSE.
This also resolve the issue of some features in the map dissappears when you zoom in.
layRoads = new
//<para>If FileBasedIndex is true, the spatial index will be read from a local copy. If it doesn't exist,
/// it will be generated and saved to [filename] + '.sidx'.</para>
/// <para>Using a file-based index is especially recommended for ASP.NET applications which will speed up
/// start-up time when the cache has been emptied.
So after you have set the FilebaseIndex to false and the .sidx file is created, you can set it back to true again.