Need Help on using substring function in webi

Hello,

I am trying to use the Substr or Left function in webi. But I am getting syntax error like Invalid data type ot this not compatible with the current settings

=Substr([order Date];1;8)

I was trying to get the below information. I have a field like below Order Date. I am trying to get Curr To Date field from Order Date. How can I get this ?

Order Date             Curr to Date

3/1/2010                   3/1/2014

3/21/2013                3/21/2014

3/4/2011                 3/4/2011

Intially I thought I will use Mon(Order Date)+Day(Order Date)+Year(curr Date) . But I could not find "Day" function in Webi . Any other ideas to get this ?