Error on NMA web app: "PDB with < 10 or > 600 c-alpha atoms not allowed"

If I try to put any PDB ID into the NMA web app (http://bio3d.ucsd.edu/nma-app/) other than the default structure, I get the following error: "PDB with < 10 or > 600 c-alpha atoms not allowed". The structure I am trying to input does have >600 c-alpha atoms, when all chains are taken together. But when I try to enter the A chain, the web app deletes what I typed and displays the error again.