If your db resides in the same folder as the exe then you don't need application.startuppath. Just use the name of the db.
Noooooooooooo!
That works untill you have not changed the parent directory. It may happen that you change it in your application without you being noticed and so it will fail. I have faced the situation and dont recommend this at all. And here was the situation.
1. Loaded the database and filled some dataset
2. Showed the report using that dataset and Crystal Reports
3. Exported the report, for example to C:\
4. Closed the report and tryed to load the database again. It failed

Here it looks in C:\ for my database cause now the parent directory has changed without you even thinking that it has changed.

So always try the full path.

Also you should be careful with Application.StartupPath as I understand it this is NOT the path to the exe but the Start In path in the shortcut. This defaults to the app.path(vb6) when the path in the shortcut is blank, however, .....
never faced any problem with it, can you bring a smaple that makes problem?