Which characters should I avoid in file names when working with LabAuthor?

As LabTutor v4 experiments are HTML based and viewed in the Internet Explorer Window, you should observe some rules to avoid crashes or unexpected behaviour in LabAuthor or LabTutor Server and Client. Experiment files like content pages, images, PDFs, video files etc will be viewed by numerous users who might use different operating systems (Windows on Mac, Windows PC) and devices (desktops, tablets, and smartphones are some examples). Problems that have been observed include unexpected LabAuthor crashing, Report pages couldn't be sent by email or experiments not loading (error 404) were due to file naming. Therefore, one should avoid common illegal filename characters (LabAuthor takes care of the proper directory names).
In LabAuthor's Rename File dialog there is a warning, if you try to use greater/smaller than sign (<,>), question mark (?), forward slash (/), back slash (\), quotation mark ("), asterisk (*), colon (:) or pipe (|). 
There will be no warnings, but don’t start or end your file name with a space, period, hyphen, or underline. Avoid to use any of the following common illegal characters/symbols. Note: the list is not exhaustive and is meant to help you avoid common errors in filenames:
pound (#), percent (%), ampersand (&), brackets ((, ), {, }), exclamation mark (!), blank space, plus sign (+), equal sign (=), at sign (@), non English characters like umlaut (ä, ö, ü) or 'sharp s' (ß), greek letters, characters with an accent (á, ë, ç etc). 
Keep a good practice by keeping file names reasonable short, using lower case and using hyphen instead of spaces and underlines.
Bad file names: Q&A Cardiology.pdf, ointment 2% cream.jpg
Good file names: q-a-cardiology.pdf, ointment.jpg