[Roy Dennis]

Are these kma or kmh types ?
If they are kma rebuilding the database should correct it.
Kmh types keep a text file (ImportedFiles.txt) in the same folder as the imported tracks which tells Hoster which files where already imported.
So check this file is present, you can open it in notepad or any word processor but don't alter it.

If you move the kmh type files to another folder or drive and not include the text file then that info is lost.
I'm not sure if rebuilding the database will restore this information but might be worth a try.

A workaround for now if you just want to import selected tracks, create a new folder and move the tracks your trying to import into it. Now brows to the new folder from the Index hard drive files dialog. The index hard drive dialog only import 99 tracks per Disc Id or Root bookId, importing more automatically increments the Disc Id or Root bookId for the next 99 tracks.
Alternatively you can use the New auto index new songs feature.
To use this feature create a new folder for storing all your new tracks in, From the Import songs menu at the bottom is a button for "select a directory for automatic indexing" brows to your new folder and always store your new tracks in there. When you next start Hoster you should see a dialog appear asking to index any new songs prss OK or later, if you ticked the box for don't ask again then it may not appear unless you select the unhide messages from the tools menu.