thank for your help,
I created project with your code, and it's worked
Then I placed this code in my project, and get the same error.
Then I use ClientFactory for creating instance of web3 ..and then it worked..
but fuctory just return new Rpc Client.
What difference between new Web3() and new RPC Client().I thought only in the url paramerter..Then I use Web3() again ..and it stayed work
this is magic)