求助网络监听程序执行时总是提示“Access Violation at address……”？？？

程序运行后，打开网络，监听数据存为了一个二进制文件，我们使用一个timer定时从文件中读取数据并更新，但是总是不断提示“Access Violation at address ……”，通过madexcept发现老是在下段程序中的“while i < n+1”的地方报错，先将程序附于下文：//实时显示数据
procedure TDTUFrm.Timer1Timer(Sender: TObject);
var
  x,n,rCnt,iRec,iDt:LongInt;
  sdt,spn:string;
  A:array of Char;
  psize:Integer;
  mypatrec:array of PatRec;
begin
   //
      x:=0;
      iRec:=0;
      psize:=0;
      //
      spn:=PathName;
      n:=ReadBcdFile(spn,pchar(A));
      //
      rCnt:=n div RawPackages;           //size of array
      SetLength(mypatrec, rCnt+1);      //获取数据信息
      while x < n+1 do
      begin
         //--------------------------------STX
         if A[x] = Char($02) then
         begin
            //-----------------------------ETX & CR
            if ((A[x+51] = Char($03)) and (A[x+52] = Char($0D))) then
            begin
               //--------------------------DateTime
               if (A[x+53] = Char($32))then
               begin
                  psize:=PackageSizes;
                  //-----------------------Endpoint
                  mypatrec[iRec].PID:=Byte(A[x+1]);
                  //-----------------------Data
                  if A[x+2] = Char($01) then
                  begin
                     mypatrec[iRec].TmpQx:=DecodeTemp(A[x+36],A[x+37]);
                     mypatrec[iRec].TmpHb:=DecodeTemp(A[x+38],A[x+39]);
                     mypatrec[iRec].TmpSb:=DecodeTemp(A[x+40],A[x+41]);
                     mypatrec[iRec].TmpDt:=DecodeTemp(A[x+42],A[x+43]);
                     mypatrec[iRec].TmpXt:=DecodeTemp(A[x+44],A[x+45]);
                     mypatrec[iRec].TmpJd:=DecodeTemp(A[x+46],A[x+47]);
                     mypatrec[iRec].TmpHj:=DecodeTemp(A[x+48],A[x+49]);
                     for iDt:=0 to 18 do
                     mypatrec[iRec].RecDt:=mypatrec[iRec].RecDt+A[x+53+iDt];
                     Inc(iRec);
                  end
                  //-----------------------Order
                  else if A[x+2] = Char($02) then
                  begin
                     //保留                  end;
               end
               //--------------------------Next STX
               else if (A[x+RawPackages] = Char($02)) then
               begin
                  psize:=RawPackages;
                  //考虑是否抛弃没有时间头的数据               end;
            end 
            //$02字节并非起始位
            else begin
               psize:=1;
            end;
         end
         else begin
            psize:=1;
         end;
         //跳过该帧
         x:=x+psize;
      end;      //数据记录
      FillDatatoGrid(mypatrec,iRec);
end;//将文件数据读入
function TDTUFrm.ReadBcdFile(filename:string; var B:PChar):LongInt;
var
   nsize:LongInt;
   tmpfile:file;
begin
   nsize:=0;
   assignfile(tmpfile,filename);
   reset(tmpfile,1);
   try
      nsize:=FileSize(tmpfile);
      getmem(B,nsize+1);
      BlockRead(tmpfile, B^, nsize);
      B[nsize]:=#0;
   finally
      closefile(tmpfile);
      Result:=nsize;
   end;
end;非常感谢！