Created Unassigned: Horizontalalign merged cells [15113]

I am having an issue getting a range of merged cells to horizontal align centered. The alignment stays as left. Here's my code.

```
ws.Cells[lStartColumn + lStartRow].Value = gPortfolioName + " - " + lTypeOfPortfolioPerf + " Performance Update";
ws.Cells[lStartColumn + lStartRow + ":" + lEndColumn + lEndRow].Merge = true;
ws.Cells[lStartColumn + lStartRow + ":" + lEndColumn + lEndRow].Style.HorizontalAlignment = ExcelHorizontalAlignment.CenterContinuous;
ws.Cells[lStartColumn + lStartRow + ":" + lEndColumn + lEndRow].Style.Font.Size = 14;
ws.Cells[lStartColumn + lStartRow + ":" + lEndColumn + lEndRow].Style.Font.Color.SetColor(bgTitleColor);
ws.Cells[lStartColumn + lStartRow + ":" + lEndColumn + lEndRow].Style.Font.Bold = true;
```