My guess would be you've reached the usage limit.
If you try this, you'll see that your loop does never abort:
lat_NW = 53.4017872352
lng_NW = 5.954233125
lat_SE = 51.9766032969
lng_SE = 10.032130575
lat_curr = lat_NW
lng_curr = lng_NW
total_calls = 0
lat_incr = -.29
lng_incr = .29
while lng_curr<lng_SE:
lng_curr = lng_NW
while lat_curr > lng_SE:
curr_location = str(lat_curr) + "," + str(lng_curr)
print curr_location
lng_curr += lng_incr
lat_curr += lat_incr
What you probably want is something like this:
...
while lng_curr < lng_SE:
lat_curr = lat_NW
while lat_curr > lat_SE:
curr_location = str(lat_curr) + "," + str(lng_curr)
...
lat_curr += lat_incr
lng_curr += lng_incr