Jerry, I was able to fix it. Here is exactly what I did:
1-Tried to log into TDAmeritade using Internet Explorer 9 that was on my 32-bit Windows 7, but could not bring up any TD pages at all. So.....
2-I downloaded IE11 and upgraded my IE9 to IE11 and rebooted computer.
3-I was now able to bring up the TDAmeritrade homepage (https://www.tdameritrade.com/home.page) using IE11.
4- I did NOT login to my TDAmeritrade account ever, just left the TD homepage up.
5-Started Medved Trader. The TDAmeritrade Authorization "secondary security check" pop-up came up again, but this time the "continue" buttons were green colored and clickable (not greyed out anymore). I was able to enter a security text code and/or the answer to a security question, which I did, and clicked the green "continue" button and got the data feed going immediately in Medved. So full success.
*Note again I did NOT have to login to my TD account through IE11 to have success. Just brought up the TD homepage without logging in to my TD account and that was apparently enough.
Thanks for your help Jerry,
-Jamie