PHP file downloading always stop at 19.8 MB size

Hi

I have PHP 5.5 on IIS 7.5 and I have problem - downloading of file always stop at downloaded file size 19.8 MB (20 772 376 bytes), sometimes downloaded file has 35,6 MB (37 350 960 bytes).

File is downloaded through

readfile($file);

I do not understand where is set the limit 19.8 MB. I already tried this

- Limit download speed to 50 or 100 kB/s, still 19.8 MB (so there is no problem with timeout somewhere).

- set <requestLimits maxAllowedContentLength="0" /> or to higher number than default 30000000, still 19.8 MB

- set in php set_time_limit(0); no change, I even set it to set_time_limit(10); (10 seconds) but downloading is working after 10 seconds

In log is this:

file.zip - 80 - Mozilla/4.0+(compatible;+Totalcmd;+Windows+7) 500 0 2147500037 120775
file.zip - 80 - Mozilla/4.0+(compatible;+Totalcmd;+Windows+7) 500 0 995 78

or

file.zip - 80 - Mozilla/4.0+(compatible;+Totalcmd;+Windows+7) 500 0 2147500037 194532
file.zip - 80 - Mozilla/4.0+(compatible;+Totalcmd;+Windows+7) 500 0 64 93

I don't understand why sc-win32-status is 2147500037

Thanks.