Those using RMark on OSX will run into a problem if they have upgraded to Yosemite. If R is launched from the system launcher, RMark won't find mark in path.
It looks like Yosemite includes a new security feature that changes the value of the PATH environment variable in certain subprocesses.
The easiest temporary workaround is to launch R from the Terminal, which overrides the security issue: "$ open /Applications/R.app"
Here, it also says all the packages that rely on PATH will need to be updated to work with Yosemite.. a note for the developers I suppose.