diff --git a/mod_mix/mod_mix.lua b/mod_mix/mod_mix.lua
index 1487848..c83a967 100644
--- a/mod_mix/mod_mix.lua
+++ b/mod_mix/mod_mix.lua
@@ -134,6 +134,14 @@ function module.load()
     module:log("debug", "Loading MIX channels done.");
 end
 
+function channel_not_found(stanza)
+    -- Wrapper for returning a "Channel-not-found" error stanza
+    return st.error_reply(stanza,
+                          "cancel",
+                          "item-not-found",
+                          "The MIX channel was not found");
+end
+
 module:hook("host-disco-items", function(event)
     module:log("debug", "host-disco-items called");
     local reply = event.reply;
@@ -151,8 +159,12 @@ module:hook("iq/bare/http://jabber.org/protocol/disco#items:query", function(eve
     local origin, stanza = event.origin, event.stanza;
     local _, channel = get_channel(staza.attr.to);
     if not channel then
-        -- TODO: Send error message
+        origin.send(channel_not_found(stanza));
+        return;
     end
+    
+    -- TODO: Maybe check permissions
+
     local reply = st.reply(stanza):tag("query", { xmlns = "http://jabber.org/protocol/disco#items", node = "mix" });
     for _, node in pairs({"urn:xmpp:mix:nodes:messages", "urn:xmpp:mix:nodes:participants", "urn:xmpp:mix:nodes:info"}) do
         reply:tag("item", { jid = channel.jid, node = node }):up();
@@ -168,14 +180,16 @@ module:hook("iq/bare/http://jabber.org/protocol/disco#info:query", function(even
     local origin, stanza = event.origin, event.stanza;
     local _, channel = get_channel(stanza.attr.to);
     if not channel then
-        -- TODO: Send error message 
+        origin.send(channel_not_found(stanza));
+        return;
     end
     local reply = st.reply(stanza):tag("query", { xmlns = "http://jabber.org/protocol/disco#info" });
-    reply:tag("identity", { category = "conference", name = channel.name, type = "mix" }):up();
-    reply:tag("feature", { var = "urn:xmpp:mix:core:1" }):up();
-    -- TODO: Do something here
-    reply:tag("feature", { var = "urn:xmpp:mix:core:1#create-channel" }):up();
     reply:tag("feature", { var = "http://jabber.org/protocol/disco#info" }):up();
+    reply:tag("identity", { category = "conference", name = channel.name, type = "mix" }):up();
+
+    reply:tag("feature", { var = "urn:xmpp:mix:core:1" }):up();
+    -- TODO: Check permissions
+    reply:tag("feature", { var = "urn:xmpp:mix:core:1#create-channel" }):up();
     origin.send(reply);
     return true;
 end);
@@ -183,11 +197,11 @@ end);
 function find_participant(table, jid)
     for i, v in pairs(table) do
         if v.jid == jid then
-            return i
+            return i;
         end
     end
 
-    return -1
+    return -1;
 end
 
 module:hook("iq-set/bare/urn:xmpp:mix:core:1:leave", function(event)
@@ -196,11 +210,16 @@ module:hook("iq-set/bare/urn:xmpp:mix:core:1:leave", function(event)
     local from = jid.bare(stanza.attr.from);
     local i, channel = get_channel(stanza.attr.to);
     if not channel then
-        -- TODO: Return error
+        origin.send(channel_not_found(stanza));
+        return;
     end
 
     local participant_index = find_participant(channel.participants, from);
     if participant_index == -1 then
+        origin.send(st.error_reply(stanza,
+                                   "cancel",
+                                   "forbidden",
+                                   "Not a participant"));
         channel:debug_print();
         module:log("debug", "%s is not a participant in %s", from, channel.jid);
         return;
@@ -230,8 +249,8 @@ module:hook("iq-set/bare/urn:xmpp:mix:core:1:join", function(event)
     local origin, stanza = event.origin, event.stanza;
     local i, channel = get_channel(stanza.attr.to);
     if not channel then
-        -- TODO: Return error
-        return
+        origin.send(channel_not_found(stanza));
+        return;
     end
     local from = jid.bare(stanza.attr.from);
     local spid = channel.spid[from] or uuid.generate(); -- Stable Participant ID
@@ -273,7 +292,8 @@ module:hook("iq-set/bare/urn:xmpp:mix:core:1:setnick", function(event)
     local from = jid.bare(stanza.attr.from);
     local i, channel = get_channel(stanza.attr.to);
     if not channel then
-        -- TODO: Return error
+        origin.send(channel_not_found(stanza));
+        return;
     end
 
     local participant_index = find_participant(channel.participants, from);
@@ -344,7 +364,11 @@ module:hook("iq-set/host/urn:xmpp:mix:core:1:create", function(event)
         node = create.attr.channel;
         local _, channel = get_channel(stanza.attr.to);
         if channel then
-            -- TODO: Return error
+            origin.send(st.error_reply(stanza,
+                                       "cancel",
+                                       "conflict",
+                                       "Channel already exists"));
+            return;
         end
 
         create_channel(create.attr.channel, from, false);
@@ -372,7 +396,8 @@ module:hook("iq-set/host/urn:xmpp:mix:core:1:destroy", function(event)
     local node_jid = string.format("%s@%s", node, host);
     local i, channel = get_channel(node_jid);
     if not channel then
-        -- TODO: Error
+        origin.send(channel_not_found(stanza));
+        return;
     end
     -- TODO: Check permissions
     
@@ -392,21 +417,24 @@ end);
 
 module:hook("message/bare", function(event)
     module:log("debug", "MIX message detected");
-    local stanza = event.stanza;
+    local stanza, origin = event.stanza, event.origin;
 
     if stanza.attr.type ~= "groupchat" then
-        -- TODO: Error handling
+        -- TODO: Is this correct?
+        origin.send(st.error_reply(stanza, "cancel", "bad-request", "Non-groupchat message"));
+        return;
     end
 
     local from = jid.bare(stanza.attr.from);
     local i, channel = get_channel(stanza.attr.to);
     if not channel then
-        -- TODO: Error handlung
+        origin.send(channel_not_found(stanza));
+        return;
     end
     
     local participant_index = find_participant(channel.participants, from);
     if participant_index == -1 then
-        -- TODO: Error not in channel
+        origin.send(st.error_reply(stanza, "cancel", "forbidden", "Not a participant"));
         return;
     end
     local participant = channel.participants[participant_index];