You may find this advice extracted from http://fragostech.com/MaemoMapper/ helpful.

Failure to Lock Troubleshooting

The GPS driver writes a almanac /var/lib/gps/nvd_data which it uses in subsequent times when the driver is started. Almanac contains orbit information on all satellites, clock corrections, and atmospheric delay parameters. It is transmitted by a GPS satellite to a GPS receiver, where it facilitates rapid satellite vehicle acquisition within GPS receivers. It appears that if the N810 is powered down during this write the almanac will be corrupted. As a result it is recommended that after terminating Maemo Mapper during a session with a successful lock you save an almanac copy for backup purposes. Open a terminal window and run:
cp /var/lib/gps/nvd_data /var/lib/gps/nvd_data.bak

If there come a time when the GPS lock won't occur even considerably past a half hour, the saved almanac should be restored. First terminate Maemo Mapper and then open a terminal window and run:
cp /var/lib/gps/nvd_data.bak /var/lib/gps/nvd_data

You will have to restart the GPS by opening the N810 Control Panel, tap GPS location, uncheck Enable GPS and tap the OK button. Lastly tap GPS location again, check Enable GPS and tap OK. When restarting your restored nvd_data almanac will be used.

This may not be a cure all but has been reported to restore correct operation in a number of instances. Hopefully this issue will be fixed or accommodated in the GPS driver.