Are you using Internet Explorer?
Please switch to Google Chrome. You can get it free here: www.google.com/chrome
Are you copy pasting styled text from a word document?
Pasting from a styled document is adding some invisible syntax and code to the editor of the custom page and is being blocked by our filters.
Please paste your text into a non styled editor like NotePad (Comes with windows), and then copy and paste again from there (this removes the styling).
Are your text color and background color the same?
Go to your invitation and try to highlight the text by click-dragging on it. It might be there but in the same color of the background (happens a lot on white pages).