Can't select SCAN ALL?

Hello, we have a Hp Color LaserJet CM1312nfi MFP. I am using a Mac on a home network to access the scanner function. The HP Scan software on my Mac does not let me select the option for SCAN ALL or even SCAN FIRST using the document feeder. I can only ever select the Flatbed SCAN button, and thus have to do each page one by one this way. I have loaded about 20 pages intot he printer's top document feeder. What am i doing wrong that I cannot scan in bulk using the feeder - why are all of the Document Feeder buttons on my HP Scan software not clickable? Thanks heaps!