In one of my projects at work, I ran into a situation where Visual Studio 2005 didn’t recognize my designer files (i.e. MainForm.Designer.vb) so all of the serialized designer code was getting stuck in a new InitializeComponent in my code file (i.e. MainForm.vb). Of course, because my Designer code was a partial class, I got an error out of it. In my experience, this behavior is sort of obscure, but here is an easy fix.

Open up the project file (which in my case was GUI.vbproj) in a text editor and do a search for your Designer file. You should see some tags that look like this:

<Compile Include="CustomControl.Designer.vb">
</Compile>
<Compile Include="CustomControl.vb">
  <SubType>UserControl</SubType>
</Compile>

Now, what it SHOULD look like is this:

<Compile Include="CustomControl.Designer.vb">
  <DependentUpon>CustomControl.vb</DependentUpon>
</Compile>
<Compile Include="CustomControl.vb">
  <SubType>UserControl</SubType>
</Compile>

Basically, my project file, for whatever reason, was missing the <DependentUpon> tag. If you add that back, Visual Studio should start behaving as expected again.