OfficeJet Pro 8720 gives "paper problem" error. There is no jam, paper doesn't get pulled from tray

[mldc9999]

OfficeJet Pro 8720 printer suddenly will not feed. Pulls paper from the tray only partially into the 2 white plastic rollers above the back of the tray.  Error message is "Paper problem" & points to area of the paper tray. Have taken the back off & cleaned rollers there, tried different paper (altho have used the same paper for years without problem). Stuck paper can easily be pulled back, shows 2 minor crimps where it came into contact with the 2 white plastic rollers.  Cannot find any other rollers accessible enough to clean.  There are no paper jams nor any pieces of paper.

[mldc9999]

UPDATE: the problem was not the pickup roller (altho I cleaned it) - there was a sticky piece of paper stuck to the plastic shield against which the pickup roller moves.  Opened the back & painstakingly picked off the stick piece - works fine now. Yay!