Run-time error '91': Object variable or With block variable not set when closing userform

In ThisWorkbook I have the following code:

Private Sub Workbook_Open()
   DashBoardUF.Show
End Sub

This loads my userform when I open my workbook as intended. But when I click the red X in the upper right corner to close the userform I get "Run-time error '91': Object variable or With block variable not set" and it points to:

DashBoardUF.Show

How do I correct this?