Cannot increase font size in ebook on Adobe Digital Editions

Is there anyone out there that can advise how to fix this.  I have previously downloaded an e-book to this program and I had no issues increasing the size of the font, This time it does not work.  I am starting to think all this technology is a waste of time and money.  Surely someone at Adobe can sort this out, isn't that their job?

Anyway, if anyone has a solution to this problem, it would be greatly appreciated to hear from you.  Otherwise, I have just wasted more time and money on a book I cannot read.