Did you try running pwd in a cell in both the new notebook and the old one? Is the current working directory the same? (See here about pwd if you are unfamiliar.)
You don’t say what type of system you are running on?
Normally, on Mac or Linux, you’d probably want that path prefaced by ~/ to make it an absolute path instead of relative, see here. Specifically with your example, you’d have more reproducibility with:
file=open(‘~/Desktop/LL/Ex/Data/ciRF_VSL2_2.csv’)