Error in ls(envir = envir, all.names = private) : invalid 'envir' argument when using dbDisconnect() after dbCommit()

Question

I am trying to update the oracle database through R by using this code:

cxn <- makeCxn(config)
    x <- try(res <- dbSendUpdate(cxn, query))
   dbCommit(cxn)
    dbDisconnect(cxn)

Then I got the error:

Error in ls(envir = envir, all.names = private) :    invalid 'envir' argument

I am using the RJDBC package and I connect to the database by instant Client.

A sample config is

config<- list(

      drv = JDBC("oracle.jdbc.OracleDriver", "<path>"),

  user = "username",
  password = "password",
  url = "xxxxxxxxxxxx"
)

My OS is windows 7.

Anyone can help? In a hurry!

Thanks