I followed the instructions in all the docs (at least I think) and I sort of have something working but have a problem with my reference

I use this to add to my linkbutton

Me.lbSubscribe.Attributes.Add("onclick", DotNetNuke.UI.Utilities.ClientAPI.GetCallbackEventReference(Me, "'test'", "successFunc", "'" & Me.lblSubscribe.ClientID.ToString & "'", "errorFunc"))

And this works up to a point

for testing I use this JS

<script>

function successFunc(result,ctx)

{

alert('recieved:' + result + '(' + ctx.id + ')');

//change pic here

}

function errorFunc(result,ctx)

{

alert('failed:' + result + '(' + ctx.id + ')');

}

</script>

however I never see ctx.id I always get an undefined - I asssume (unless I misread) that the ctx.id would be the clientid of the linkbutton - what might I be doing wrong here?

I am not sure what you say was fixed and what you are now having problems with.  Are you getting your alerts?  If so what do they say?  Your original registering of the callback was using the clientid as the param, so I am not sure why you are using ctx.id now... should just be ctx.

Let me suggest downloading the HelloAJAX sample from the ClientAPI project downloads page.

Glad to hear you figured it out.

For clarification, your original post stated this as your callback registration

Me.lbSubscribe.Attributes.Add("onclick", DotNetNuke.UI.Utilities.ClientAPI.GetCallbackEventReference(Me, "'test'", "successFunc", "'" & Me.lblSubscribe.ClientID.ToString & "'", "errorFunc"))

You are specifying the lblSubscript.ClientID property (a string) as your context.  This is the value that will be associated to the ctx variable on the client.  The samples that the documentation includes is

which passes this as the context variable.  In this case it represents the object that triggered the event (mybutton).