I believe the problem may be with the function crypt ().

crypt() is a glibc function, and you are getting this error because crypt() is returning NULL.  This indicates some sort of error.  Maybe there's a problem with the password you're trying to set.

The code in yp-tools you're hitting is in yppassword.c (no surprise) in main():
      crypted_pass = crypt (buf, salt);
      if (crypted_pass == NULL);
        {
         printf (_("crypt() call failed - password unchanged.\n"));
         return 1;
        }

      yppwd.newpw.pw_passwd = strdup (crypted_pass);

Assignee: bugsquad => tmb
Source RPM: yp-tools-2.14-3.mga4.i586.rpm => glibc

Mageia 4 changed to end-of-life (EOL) status on 2015-09-19. It is is no longer 
maintained, which means that it will not receive any further security or bug 
fix updates.

Package Maintainer: If you wish for this bug to remain open because you plan to 
fix it in a currently maintained version, simply change the 'version' to a later 
Mageia version.

Bug Reporter: Thank you for reporting this issue and we are sorry that we weren't 
able to fix it before Mageia 4's end of life. If you are able to reproduce it 
against a later version of Mageia, you are encouraged to click on "Version" and 
change it against that version of Mageia. If it's valid in several versions, 
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Example: it's valid in cauldron and Mageia 5, set to cauldron and add MGA5TOO.

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As announced over a month ago, Mageia 4 changed to end-of-life (EOL) status on 2015-09-19. It is is no longer maintained, which means that it will not receive any further security or bug fix updates.

This issue may have been fixed in a later Mageia release, so, if you still see it and didn't already do so: please upgrade to Mageia 5 (or, if you read this much later than this is written: make sure you run a currently maintained Mageia version)

If you are able to reproduce it against a maintained version of Mageia, you are encouraged to 
1. reopen this bug report, by changing the "Status" from "RESOLVED - OLD" to "REOPENED"
2. click on "Version" and change it against that version of Mageia. If you know it's valid in several versions, select the highest and add MGAxTOO in whiteboard for each other valid release.
Example: it's valid in cauldron and Mageia 5, set to cauldron and add MGA5TOO.
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If you see a similar issue, but are _not_sure_ it is the same, with the same cause, then please file a new bug report and mention this one in it (please include the bug number, too). 


If you would like to help fixing bugs in the future, don't hesitate to join the
packager team via our mentoring program [1] or join the teams that fit you 
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[1] https://wiki.mageia.org/en/Becoming_a_Mageia_Packager
[2] http://www.mageia.org/contribute/

Status: NEW => RESOLVED
Resolution: (none) => OLD