SAX Parser PHP no memory at line x

I m using SAX Parser with php to parse a 1.2GB xml file and the results are written in a txt file. After several minutes I get an error of "no memory at line x". When this is done the text file output is only a few kB (whereas the expected output file could well exceed several MB in size) and has stored very few of the information needed. I m running this project on a windows 7 64bit system with i7 processor and 18 GB RAM, using xampp, but I have also run it at a 32bit system with the same results. I have modified the php.ini with these commands:

ini_set('max_execution_time', 72000); 
ini_set('memory_limit','13056M');
ini_set('realpath_cache_size','13056000k');
ini_set('max_input_time','-1');

Is there something I should modify in php.ini? Could this be some kind of buffer overflow when the code doesn't find the filtered data to parse and only reads "junk" data? Could this be an error caused by the OS file size restrictions? Has anyone else solved anything similar? Thank you in advance.