First verify that the file exists. Then, try with the absolute path of that file. Do you get same error then?
@FinnW, in answer to your post below:
Absolute path is the full path. So, on Unix systems, that will be starting from root directory, and windows, starting from the main drive (C, D, etc)
If you are on Mac, try something like this ~/Desktop/StudentRevertantFrequencies.xlsx. Or, go to finder and note the path via right click and get info for file.
If you are on windows, you can get the path via Properties after right click on the file.