I guess I found out the answer by playing around with relative versus absolut paths. I thought that by setting a file structure with the main experiment file on top of the file structure and adding all other questionnaires and images in subfolders I would be able to use relative paths for all the questionnaires. However, I found out that I need to use absolut paths for all questionnaires that are in subfolders which call for bitmaps that are in sub-subfolders (e.g., experiment\questionnaire1\bitmap1). Therefore, if your questionnaire is in a subfolder from the main experiment file, you have to set absolut paths to all your questionnaires when they access bitmaps.

This is a hassle when I need to move the entire experiment onto another computer which has a different file structure. Maybe it's possible to keep it relative but I don't know how.