HyperLink Control NavigateUrl parsing error.

Dear all,
I try to add to the navigate url a value from an other control, here on dropdownlist, to the existing url :

<asp:HyperLink runat="server" ID="hyperLinkActions" Text="Actions" NavigateUrl="<%# "Edit.aspx?scriptId=" + elementsToEdit.SelectedValue%>"></asp:HyperLink>
Now this gives me a parsing error, if possible no postback has to be triggerd to change the navigate url.
Thanks

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