knit to HTML button not working in Rstudio on Ubuntu 12.04

knit to HTML button not working in Rstudio on Ubuntu 12.04

I have recently installed the latest versions of R (3.0.1) and RStudio
(0.97.551) on Ubuntu 12.04, and I find that whereas the knit2html function
work just fine on an Rmd document, the button Knit HTML does not (neither
does RStudio's keyboard shortcut). This seems to be the opposite of the
problem that some people have reported (not on Ubuntu, though) hwere the
button works and the function doesn't.
Has anyone encountered and/or fixed this issue?
Thanks, Homer White