Which mirror are you using?

I have tried the following mirrors, all produce the same problem
us2.php.net  	Hurricane Electric
www.php.net 	Yahoo! Inc.
ar.php.net  	BairesWeb.com
ar2.php.net 	XMundo Hosting Solutions
ca.php.net  	easyDNS
ca3.php.net 	egateDOMAINS
uk.php.net  	Kewlio.net Limited
uk2.php.net 	Camel Network

bjori@lindsay tmp$ for i in us2 www ar ar2 ca ca3 uk uk; 
do fetch -o $i.chm 
http://php.net/get/php_manual_en.chm/from/$i.php.net/mirror 
&& md5 $i.chm; done
us2.chm                                       100% of 4970 
kB  113 kBps 00m00s
MD5 (us2.chm) = 60c672355cd0d227adb0646370bfc14a
www.chm                                       100% of 4970 
kB  343 kBps 00m00s
MD5 (www.chm) = 60c672355cd0d227adb0646370bfc14a
fetch: 
http://php.net/get/php_manual_en.chm/from/ar.php.net/mirror: 
No address record
ar2.chm                                       100% of 4970 
kB  154 kBps 00m00s
MD5 (ar2.chm) = 60c672355cd0d227adb0646370bfc14a
ca.chm                                        100% of 4970 
kB  190 kBps 00m00s
MD5 (ca.chm) = 60c672355cd0d227adb0646370bfc14a
ca3.chm                                       100% of 4970 
kB   43 kBps 00m00s
MD5 (ca3.chm) = 60c672355cd0d227adb0646370bfc14a
uk.chm                                        100% of 4970 
kB 1182 kBps
MD5 (uk.chm) = 60c672355cd0d227adb0646370bfc14a
uk.chm                                        100% of 4970 
kB 1200 kBps
MD5 (uk.chm) = 60c672355cd0d227adb0646370bfc14a

Can't reproduce this. Works on all of the mirrors you 
listed except from ar.php.net

I've confirmed the checksums also, but actually opening php_manual_en.chm on Windows does not show any documentation, just a standard IE 404.

Reclassified as a documentation problem (I misunderstood 
it as website/mirror problem).

Assigning to the chm wiz.

Note: xchm on mac opens this file, but as a blank page.

I can confirm that the file is broken and I'll look into this on Monday. In the meantime, try the Extended CHM. This is the same manual but also includes the user notes.

You can download this other file from http://www.php.net/get/php_manual_chm.zip/from/a/mirror

This will be a ZIP file with several files in it. Unzip it all into a single location. Run the php_manual_prefs.exe to setup your options and then open the php_manual_en.chm.

This bug has been fixed in the documentation's XML sources. Since the
online and downloadable versions of the documentation need some time
to get updated, we would like to ask you to be a bit patient.

Thank you for the report, and for helping us make our documentation better.