ZipArchive doesnt work for large files

Hi, I am having problems using any of the ZipArchive functions for files above a certain size. For example creating a new zip and adding 1 file works fine for files that are only a few kb, but when I tried a slightly large one (about 60k) the zip became corrupt. Here is the code im using: $zip = new ZipArchive(); $zip->open('c:/uploads/test.zip',ZipArchive::CREATE); $zip->addFile('c:/uploads/uk_natural.shp','uk_natural.shp'); $zip->close(); This creates the zip archive but when I try and extract the file I get the error: "C:\uploads\test.zip: CRC failed in uk_natural.shp. The file is corrupt". Does anyone know why this is being corrupted?