replace error

Hi in sample.aspx, I have the below code,

I want to replace blank with "-" and replace with / to "-"

  <% dim sp as string%>
  <% sp = Replace(Eval("Name"), " ", "-")%>
   <% sp = Replace(sp, "/", "-")%>

       <a href='/store/<%=sp %>/<%# Eval("Id") %>'>  

Error is on the aove statement the erors says BC30451: 'sp' is not declared. It may be inaccessible due to its protection level.

Thanks