What do you mean with "reload"? Do you have loaded the original db manually or do you have laded a backup of your database? In the first case that should not happen, I've done so many times when handling multiple databases. For the second case you have to know that the internal backup procedure of XMM only saves the .mdb and not all the pics. Have a look at the backup section of the wiki for more details. Or are only the thumbnails no longer associated? On that I'm not really the man to answer but I think there exists an option for rebuilding thumbnails. As said: I'm not sure if it reallly exists and where you can find it.
In order to achieve what is possible, you have to try the impossible over and over again. Hermann Hesse