You are not specifying in your URL which object you want to create the new Record for.
So assuming it is Account, it should be
PageReference('\001\e?retURL='+Apexpages.currentPage().getParameters().get('retURL')+'&recordType='+RecordTypeId);
Or alternatively create a dummy object of the required object ( say account ) and use the standard controller itself as shown below.
Account account = new Account();
account.RecordTypeId = someId;
PageReference pg = new ApexPages.StandardController(account).edit();
Change the above for any of the other custom or standard objects.
/001/e
. Similarly find the prefix of the object you want to create and accordingly modify the URL. – AslamK Oct 13 '15 at 13:47