What steps will reproduce the problem?
1. Embed the library per the documentation.
2. Call self:UserInfo('SomeoneNotOnline', {callback='handleUserData'})
3. handleUserData will get called with nil as the first parameter.

What is the expected output? What do you see instead?
I'm expecting something along the lines of
{ Name='SomeoneNotOnline', Online=false }

What version of the product are you using?
2.0-2.0.2

Do you have an error log of what happened?
Not one that's very useful.

Please provide any additional information below.
This patch fixes the bug:

--- LibWho-2.0.lua.orig      2009-04-14 12:40:18.000000000 -0400
+++ LibWho-2.0.lua 2009-05-04 00:47:31.000000000 -0400
@@ -178,7 +178,7 @@
                                self:RaiseCallback(args, self.Cache[args.name].data)
                                return false
                        else
-                               return self:DupAll(self:ReturnUserInfo(name))
+                               return self:DupAll(self:ReturnUserInfo(args.name))
                        end
                elseif(self.Cache[args.name].valid == false)then
                        -- query is already running (first try)
@@ -426,7 +426,7 @@
                end
                dbg('Info(' .. name ..') returned: ' .. (self.Cache[name].data.Online == false and 'off' or 'unkn'))
                for _,v in pairs(self.Cache[name].callback) do
-                       self:RaiseCallback(v, self:ReturnUserInfo(v.Name))
+                       self:RaiseCallback(v, self:ReturnUserInfo(v.name))
                end
                self.Cache[name].callback = {}
                self.CacheQueue[self.Args.query] = nil

Thanks for a great library, by the way. It has saved me a lot of time :)