[R] RWebdriver and RSelenium returns the same error while trying to connect the java server

[PO SU]

Dear expeRts,
   when i using RWebdriver and RSelenium , 



> require(RSelenium)
Loading required package: RSelenium
> remDr <- remoteDriver(remoteServerAddr = "localhost" 
+                       , port = 4444
+                       , browserName = "firefox"
+ )
> remDr$open()
[1] "Connecting to remote server"



Error: 	 Summary: UnknownError
 	 Detail: An unknown server-side error occurred while processing the command.
 	 class: org.openqa.selenium.firefox.NotConnectedException


from the cmd lines, it show "unable to connect 127.0.0.1 7055 after 45000ms "


i don't know why, is there anybody who happens to know it ?
--

PO SU
mail: desolator88 at 163.com 
Majored in Statistics from SJTU