Once you have saved the filre, you still have to go through the installation process to extract the data.
Use windows search to look for all occurances of Navdata db.3 to see where they all are. You obviously have more than one Airnav version and it is going to the wrong one for the data.
If you installed the origional disk and then installed the 4.03 or 3.13 versions you will have two versions in different places. Yoy require to find the path to the version you use and only go as far as Airnav Systems Radarbox, dont go as far as data as the innstaller puts it in the data folder. If you find the correct and wrong Navdata you could always moves the new one over and replace the older version with the new one.
What version of windows do you use.
Alan