Unfortunately, Logger Pro can only export one data set or track into a single Google Map. The workaround is to bring in each track one at a time, copying and pasting them into a single data set, appending as you go. To do this:
1. Import one track into Logger Pro.
2. Highlight the data in the table and choose Copy from the Edit menu.
3. Open a new Logger Pro file (if it asks whether you want to bring in data this time, say no).
4. Click in the first data cell in the table and choose Paste from the Edit menu. Your first track is now in the new file.
5. Double-click each column heading and rename them with Lat, Long, etc.
5. Save this file with a unique name.
7. Do a File-->New and when prompted, import the second track.
8. Highlight the data in the table and choose Copy from the Edit menu.
9. Open your saved file.
10. Click in the first empty cell of the first column of the data table and paste your data from the second track. Save.
11. Repeat steps 7-10 for each track until you have them all pasted in.
Now export to Google Maps.