Can I set the maxlength of a textbox to an integer property of a shared (static) class?

Whenever I use a textbox that expects a URL input, I want to set its MaxLength to 330.  
So I made a class property (in a shared class) called 'urlmaxlength', and had it return 330.
Then in every textbox that expects a URL, I set MaxLength as follows:
<asp:TextBox ID="TextBoxUtubeCode" runat="server" MaxLength="<%=ClassStrings.urlmaxlength %>" Width="294px"></asp:TextBox> It does not work.  
In fact it gives an error message.
Why is that?
Thanks,
Gideon