Warning message when starting RStudio

Hi list

Recently, when starting up RStudio, the following warning is being 
displayed:

"Error in tools:::httpdPort <= 0L :
  comparison (4) is possible only for atomic and list types"

I think that this is specific to RStudio because starting R in a 
terminal window doesn't produce this message.

Does anyone have an idea on how to clear the conditions that are giving 
rise to this warning?

Many thanks
Sun