Problem Override method

I’m trying to override a method using this code below 

using System;

using PX.Data;

using PX.Common;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using PX.Objects.CS;

using PX.Objects.GL;

using PX.Objects.CM;

using PX.Objects.TX;

using PX.Objects.AP;

using PX.Objects.AR;

using PX.Objects.IN;

using PX.Objects.GL.FinPeriods;

using PX.Objects;

using PX.Objects.CA;

namespace PX.Objects.CA

{

    public class CAReleaseProcess_Extension : PXGraphExtension<CAReleaseProcess>

    {

        public delegate IEnumerable<Batch> ReleaseDocProcDelegate<TCADocument>(JournalEntry je, ref List<Batch> batchlist, TCADocument doc)

                where TCADocument : class, ICADocument, new();

        [PXOverride]

        public IEnumerable<Batch> ReleaseDocProc<TCADocument>(JournalEntry je, ref List<Batch> batchlist, TCADocument doc, ReleaseDocProcDelegate<TCADocument> baseMethod)

                where TCADocument : class, ICADocument, new()

        {

            batchlist = new List<Batch>();

            //doc = new TCADocument ();

            return baseMethod(je, ref batchlist, doc);

        }  

    }

}

But I'm getting this error: 

Validating Extensions

Method System.Collections.Generic.IEnumerable`1[PX.Objects.GL.Batch] ReleaseDocProc[TCADocument](PX.Objects.GL.JournalEntry, System.Collections.Generic.List`1[PX.Objects.GL.Batch] ByRef, TCADocument, ReleaseDocProcDelegate`1) in graph extension is marked as [PXOverride], but its signature is not compatible with original method

Validation failed.