Can't add a specific investment

When I downloaded transactions from my broker this morning, I had a few new securities to add. I was able to add most of the new securities, but Quicken won't add Deere & Co (symbol DE) to my Security List. "Unidentified Security" was downloaded into the security name, while 'Deere and Co' was downloaded into the Memo line. I have tried to add DE several times, through both the Security List (both automatically and manually) and through editing the downloaded transaction. When I enter the DE symbol into the "Add Security to Quicken" screen, DE is listed. After I highlight it and click 'Next', I get the "Quicken will add the following information for the new security Deere & Co.". So far so good. I click 'Done' and get the little blue spinning circle for a few seconds. It stops, but DE is not in the Security List. I have closed and reopened Quicken multiple times and even rebooted my computer between my attempts to add DE, but nothing changes. It is not hidden. The process I described above happens each time, so Quicken has no record of DE being added (but not displayed). I validated the file, but that didn't help. I’m not a techno whiz, so I don’t know what else to do. Any thoughts? Thanks in advance.