I will do my best to help you fax a scanned document but I want to make sure I completely understand.
1. When you scan an image, you use the HP scanning software to scan in a document, but what is the title of the program you are using to fax to the printer (Solution Center, Adobe Reader, Windows Media, etc)?
2. Can you fax normally?
3. Are the documents you are trying to fax .pdf, .tiff, etc?
4. How is the printer connected to the computer (USB or wireless)?
5. Has this ever worked for you before?
Here is a document that may be of some assistance. --Fax Scan Failed-- If this does not help you, please answer the questions above so I can be of better assistance.