Under certain circumstances you might find that your custom experiment works fine during the students' course using LabTutor Client, but if you want to review the Student Data from within the LabTutor Server you see an error message, either a generic "HTTP 404: Not found" error or a LabTutor File not found error, respectively:
The most likely reason is a conflict with file naming of the report page in LabAuthor. If the report page file name contains a space like in report page.html or other special characters such as () # or %, you will observe the above error message.
To rectify this, open your experiment in LabAuthor and rename the report page to a valid name for example report.html. To do so right-click on the report page in the left panel and choose "Rename File..." from the context menu. Change the name and confirm by pressing OK. Go to Edit > Experiment Properties... and increase the version number. Save the Experiment and then save an Experiment Installer. When uploading and installing the new experiment to the LabTutor Server, please make sure to check 'Replace existing versions in Course lists'.
Please see also the related information "Which characters should I avoid in filenames when working with LabAuthor?"