So, given that today's date is
05.11.2015, if a sheet named "Data Input
05.11.2015" doesn't exist, you'll get a 'subscript out of range' error... There's also the question of whether the Date keyword on your system returns dates expressed in the DD.MM.YYYY format.
Even so, you shouldn't need to activate a worksheet to work with it. For example:
Code:
Sub Test()
Dim v_Sheetname As String
v_Sheetname = "Data Input " & Format(Date, "DD.MM.YYYY")
MsgBox Sheets(v_Sheetname).Range("A1").Value
End Sub