[R-pkg-devel] no visible binding for '<<-' assignment note

Dear all,
In the last submission of my package the CRAN gave this note: "Check: R code for possible problems, Result: NOTE: no visible binding for '<<-' assignment..."

How can I bypass this note?

This is the local function which cause this note:
  dnormfun <<- function(muvalue, sigmavalue, aNumber = gridY[i] ){
    force(aNumber)?
    ansvalue=dnorm(aNumber,muvalue,sqrt(sigmavalue))?
    return(ansvalue)?
  }?

The package can run normally at my machine. Any suggestion?

Thanks,

Weimin