Hello, In the past I have used intensively the mtrace function from the debug package, but now with my actual version of R(2.8.1) , it is impossible to use it anymore. I've updated all my packages, and I don't understand how solve this problem... Here is an example code : > foo<-function(){cat("Test Function")} > mtrace(foo) > foo() # A tcl/tk windows open and close immediately.... Erreur dans FUN("l"[[1L]], ...) : l'argument "l" est manquant, avec aucune valeur par d?faut #argument "l" is missing without default value... I've tried to look in with traceback(), but it does not help me. > traceback() 21: FUN("l"[[1L]], ...) 20: lapply(savers, get, envir = nlocal.env) 19: mlocal(index(nchar(names(line.list)) > 0)[l] - 1) 18: screen.line(lno) 17: assign("answer", { Here is some technical informations : > Sys.info() sysname release version nodename "Windows" "Vista" "build 6001, Service Pack 1" "XXX-HOME-VISTA" machine login user "x86" "xxx" "xxx" > R.Version() $platform [1] "i386-pc-mingw32" $arch [1] "i386" $os [1] "mingw32" $system [1] "i386, mingw32" $status [1] "" $major [1] "2" $minor [1] "8.1" $year [1] "2008" $month [1] "12" $day [1] "22" $`svn rev` [1] "47281" $language [1] "R" $version.string [1] "R version 2.8.1 (2008-12-22)" Sincerely