One of my customers is migrating all the machines and infrastucture servers to the Active Directory. More than one hundred users with firstname.lastname usernames. There are some apache web servers using famous mod_ntlm.

Although it’s a very old module, there is no need to replace it, because it works fine. But for some users they’ve got messages like this in the apache error_log:

[Thu Mar 30 19:44:41 2006] [error] [client 192.168.0.1] ntlm_decode_msg failed: type: 3, host: "OURHOST", user: "", domain: "OURDOMAIN", error: 16
[Thu Mar 30 19:44:41 2006] [error] [client 192.168.0.1] missing/corrupt NTLM header 165569360 26048

The solution was simple (but I was unable to find it in bug reports or anywhere else), some usernames were too long for mod_ntlm. So, edit the MAX_USERLEN constant in file ntlmssp.inc.c to satisfy your needs, re-build and re-install the module.