[Jоnny]

Windows Server 2003
Left 4 Dead 2
cURL 1.2.0.0 (1.3 wont work)

left4dead2/addons/sourcemod/data/steam-group-admins-http/temp.xml

<?xml version="1.0" encoding="UTF-8" standalone="yes"?><memberList>
<groupID64>103582791431374955</groupID64>
<groupDetails>
        <groupName><![CDATA[L4C.Admins]]></groupName>
        <groupURL><![CDATA[L4CA]]></groupURL>
        <headline><![CDATA[]]></headline>
        <summary><![CDATA[No information given.]]></summary>
        <avatarIcon><![CDATA[http://media.steampowered.com/steamcommunity/public/images/avatars/fe/fef49e7fa7e1997310d705b2a6158ff8dc1cdfeb.jpg]]></avatarIcon>
        <avatarMedium><![CDATA[http://media.steampowered.com/steamcommunity/public/images/avatars/fe/fef49e7fa7e1997310d705b2a6158ff8dc1cdfeb_medium.jpg]]></avatarMedium>
        <avatarFull><![CDATA[http://media.steampowered.com/steamcommunity/public/images/avatars/fe/fef49e7fa7e1997310d705b2a6158ff8dc1cdfeb_full.jpg]]></avatarFull>
        <memberCount>7</memberCount>
        <membersInChat>0</membersInChat>
        <membersInGame>2</membersInGame>
        <membersOnline>1</membersOnline>
</groupDetails>
<memberCount>7</memberCount>
<totalPages>1</totalPages>
<currentPage>1</currentPage>
<startingMember>0</startingMember>
<members>
<steamID64>76561197993799724</steamID64>
<steamID64>76561198001361766</steamID64>
<steamID64>76561198029715727</steamID64>
<steamID64>76561198016886882</steamID64>
<steamID64>76561198031498488</steamID64>
<steamID64>76561198021066932</steamID64>
<steamID64>76561198037275727</steamID64>
</members>
</memberList>

Is there anything strange about your file permissions

no, full access