HI Nikos,
Which version of R are you using?
withVisible is part of the R base package, so it should be available?
Also, which OS are you working in?
Carson
--
Carson J. Q. Farmer
ISSP Doctoral Fellow
National Centre for Geocomputation (NCG),
Email: Carson.Farmer at gmail.com
Web: http://www.carsonfarmer.com/
http://www.ftools.ca/