Error on image stream using ojw.dev.openstreetmap.org

Hi!

I'm Gabriel, an Argentinian programmer (please excuse my english).

I'm using the service published on http://ojw.dev.openstreetmap.org/ to get maps for an application, on regular time intervals. From some days i've been detecting some errors in my log when loading the image data, on a .NET component designed to such end. These errors are related to the info on the downloaded stream (the image). After some hours of debugging, i've noticed that if i call this url:

http://ojw.dev.openstreetmap.org/StaticMap/?lat=-38.033819065207&lon=-57.570014370957&z=15&mlat0=-38.033819065207&mlon0=-57.570014370957&layer=mapnik&w=350&h=250&filter=grey&show=1

... i've got an incorrect response, in terms of image data. If I change the zoom parameter (the z=15 part of the url) from 15 to 16, the service works as expected.

After looking the raw data of the image in an hex editor, i've notice this error at the firsts lines of the stream:

Warning: imagecreatefrompng(): '../../data/tiles/mapnik151114420132.png' is not a valid PNG file in /home/ojw/publichtml/StaticMap/map.php.inc on line 49

If i remove this bytes from the stream, i got a "correct" image data. When open it from a image browser, the image appears correct but with a grey block at the lower right part of it.

What can i do to fix it?

Thanks in advance!