Label does not exist in current context on ASP.NET page

There are many questions with same name as this one, but I haven't found solution.

MasterPage.master:

<div id="dateShow"> 
    <asp:Label ID="lblDateShow" runat="server"></asp:Label>
</div>

MasterPage.master.cs:

protected void Page_Load(object sender, EventArgs e)
{
    lblDateShow.Text = DateTime.Now.ToShortDateString();
}

It happens on building and show me the error, but if I run without building (before run-->no build) it shows me the date. It happens only in master page with all controls that I want to add, on other pages all work fine. What could be the problem?

Error Message is:

Error 1 The name 'lblDateShow' does not exist in the current context

Long discription:

Warning 2 The type 'MasterPage' in 'c:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\thegame\6da1e5d1\9152b07\App_Web_tmu2ya5i.4.cs' conflicts with the imported type 'MasterPage' in 'c:\Windo开发者_JAVA技巧ws\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\thegame\6da1e5d1\9152b07\App_Web_masterpage.master.cdcab7d2.k9aa16y-.dll'. Using the type defined in 'c:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\thegame\6da1e5d1\9152b07\App_Web_tmu2ya5i.4.cs'. c:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\thegame\6da1e5d1\9152b07\App_Web_tmu2ya5i.4.cs

I tried to delete Temp files, didn't help..

UPD I solved that problem. I Had another masterpage2.master and somehow he did all the problems. When I created label or other control, he was declared in second master page, I don't know how can it be))

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It happend with me and I took some days until discovery that I had one more page with the same code behind (CodeFile="PageName.aspx.cs") wich did not have the control ID. I just deleted it and the problem was deleted together.

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If lblDateShow is in the markup of your master page, but it appears not to exist in the code-behind file, then it is most likely a problem with the designer.cs file for your master page. Is lblDateShow instantiated there? If not, you will need to regenerate your designer file or add the Label manually.

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Try putting it in the right namespace. That was my issue