Help with GPS

Hi all,
in my application I simply activate GPS in internal mode:

adl_gpsSubscribe ( GpsHandler, 1);

ascii Latitude[50];
ascii Longitude[50];
wm_sprintf ( Latitude, GPSData->Position.latitude);
wm_sprintf ( Longitude, GPSData->Position.longitude);
wm_sprintf(Buff,“Latitude: %s ; Longitude: %s\r\n”,Latitude, Longitude);
adl_atSendResponse ( ADL_AT_UNS, Buff );

during first 5 minutes i receive the coordinates normally:

Latitude: 0803.81961 ; Longitude: 03452.69350
Latitude: 0803.81962 ; Longitude: 03452.69349
Latitude: 0803.81963 ; Longitude: 03452.69349
Latitude: 0803.81963 ; Longitude: 03452.69348
Latitude: 0803.81964 ; Longitude: 03452.69348

but after that:

Latitude: ; Longitude:
Latitude: ; Longitude:
Latitude: 0803.81942 ; Longitude: 03452.69422
Latitude: 0803.81940 ; Longitude: 03452.69423
Latitude: ; Longitude:
Latitude: 0803.81944 ; Longitude: 03452.69424
Latitude: ; Longitude:
Latitude: ; Longitude:
Latitude: 0803.81918 ; Longitude: 03452.69412
Latitude: 0803.81935 ; Longitude: 03452.69407

after some time receiving wrong coordinates, i receive them right again, and so on…

the antenna is not moving and the module(Q2501B) is being supplyed by a relyable power source.

any ideas?

Sérgio

see also: http://www.wavecom.com/modules/movie/scenes/forums/viewtopic.php?t=1160