glmnet : Error in validObject(.Object) :

Could any one help ? I start to learn the glmnet package. I tried with 
the example in the manual.

x=matrix(rnorm(100*20),100,20)
 y=rnorm(100)
 fit1=glmnet(x,y)


When I tried to fit the model, I received the error message:

Error in validObject(.Object) :
  invalid class "dgCMatrix" object: row indices are not sorted within 
columns

Thank you very much!