Label not building in codebehind? But control is in ASPX and autocomplete recognizes it

This is a very complex webform, but hopefully it's an easy fix.
We have Home.aspx and Home.aspx.cs. Home.aspx uses a label control:
<asp:HyperLink runat="server" ID="hlForSale" CssClass="linkBorder0" ImageUrl="OurSite_images/for_sale_Original.gif" NavigateUrl="~/Home.aspx?AdType=1"></asp:HyperLink> During the build, the compiler does not recognize the control even though the autocomplete does. The error is the name 'hlStart' does not exist in the current context
What can the problem be? The odd thing is that this code is copied to our server and it actually runs (ie. I see Home.aspx in browser and everything works). But when I copy the code to my PC and try to build, I get the error.
Any help is appreciated.