It may help to define what you are trying to do better, before hunting for errors in code. Perhaps your approach is sound, but not in line with your functional expectations.

Interpretation: You are trying to find out if $author is in the @admin_users list, and return true/false accordingly.

if (grep { lc eq lc($author) } @admin_users)
{
     print "$blah";
}
else
{
     print "$uber_blah";
}
[download]

Of course, I would make sure that you prune your @admin_users list, making it all neat and tidy before feeding it to this routine. For example, you will want to strip off extraneous characters, such as dangling spaces and newlines.

@admin_users = map { s/\s+//; $_ } @admin_users;