Incorrect parameter issue when calling requre("socket.core") on Lua 5.1.2 + LuaSocket 2.0.2 in Windows

[p o <opluax@...>]

Hi

Now I'm creating a program with Lua + LuaSocket. Lua is working well
on my program.
Now I'm trying to add LuaSocket support.
I could build LuaSocket successfully, I got socket.dll and mime.dll
(on Windows), built by VS2008 without errors.
And I remane them to core.dll and put correct places, of course I
install other modules such as socket.lua etc.
I did all install steps however Lua displays following error.

--- script start ---
socket = require("socket")
--- script end ---

Error message: "The parameter is incorrect"
On line 13 in "socket.lua" which is "local socket = require("socket.core")"

The target file "socket/core.dll" exist correct directory.
(because Lua can find "socket.lua")

Do you know how to solve this problem and what does this means?
Is it LuaSocket issue or dll build issue or Lua?
Please help me.

Best regards
Beck.