problem on Solaris 8

[Charlie Reitsma]

I have sudo 1.6.6 installed on Solaris 8. The sudoers file contains:
root ALL=(ALL) ALL
%sysadmin ALL=ALL

One member of the sysadmin group has the problem of being prompted for a 
password but it won't be accepted. When this happens she only has to 
press "Enter" to have her command executed with root privilege. Anything 
done when this is happening is not logged. Unfortunately, it does not 
happen every time she uses sudo.

None of the other members of sysadmin have the problem. Their passwords 
are always accepted/required. Nor does it appear that anyone outside of 
the sysadmin group can use sudo at all.

Any ideas what I should look for?
#define HAVE_GETSPNAM 1
is in config.h