Windows Defender Offline definitions out of date

Windows 7 64 Bit.  I have been using Windows Defender Offline on a USB thumb drive (4 GB, uses less than 1 GB) for years without problem.  Last week updating Windows Defender Offline definitions to an already working USB thumb drive seemed to install correctly.  When I boot to the USB thumb drive the program boots and runs but I get the message the "definitions out of date", and it will not scan the computer.  I tried formatting USB thumb drive and then installing the whole Windows Defender Offline with definitions instead of just updating the definitions to the already working USB thumb drive.  Everything went correctly, the size of the download appeared to be correct.  I booted to the USB thumb drive and still got the message "definitions out of date".  Since the Windows Defender Offline program started offline, and was installed onto a completely formatted USB thumb drive, it must have downloaded and installed correctly but the definitions are still "out of date".  Are the definitions being updated by Microsoft or has the program been discontinued?