When a @RemoteAction method throws an exception due to a programming error or other failure, the Apex stack trace is returned to the browser within the event object. Inspect the stack trace in a JavaScript debugger console or use it in the error handling of your response callback function.
<script type="text/javascript"> function getRemoteAccount() { var accountName = document.getElementById('acctSearch').value; Visualforce.remoting.Manager.invokeAction( '{!$RemoteAction.MyController.getAccount}', accountName, function(result, event){ if (event.status) { document.getElementById('acctId').innerHTML = result.Id document.getElementById('acctName').innerHTML = result.Name; } else if (event.type === 'exception') { document.getElementById("responseErrors").innerHTML = event.message + "<br/>\n<pre>" + event.where + "</pre>"; } else { document.getElementById("responseErrors").innerHTML = event.message; } } ); } </script>