Great. Please mark your answer as the solution for the benefit of those to follow. (No false modesty; it closes the loop in the simplest possible term and serves as a user-to-user alert: make sure the file is in your current working directory.
I should have mentioned the easy way to check
dir()
(if it doesn't show up then the R session can't see it without a path, such as data/file.csv for a subdirectory in the working directory, or a full pathname outside.)