I have a package which contains a csv file which I put in inst/extdata per R-exts. This file is needed for the vignette. If I Sweave the vignette directly, all works well.
Have you tried using system.file instead of hardcoded relative paths?
system.file
EC1 <- dot2HPD(file = system.file("inst", "extdata", "E_coli", "ecoli.dot", package = "your_package+name")) node.inst <- system.file("inst", "extdata", "E_coli", "NodeInst.csv", package = "your_package_name")