The parent file, 'file1', for file 'file2' cannot be found in the project file
The project system cannot find a node corresponding to a file.
Dependent files are persisted in the project file by adding a DependentUpon attribute to the <File> node. For example:
<File RelPath = "Form1.resx" SubType = "Code" BuildAction = "EmbeddedResource" DependentUpon="Form1.vb" />
This will make Form1.resx appear below Form1.vb in the project hierarchy.
This error is most likely caused by editing the project file by hand.
To correct this error
Edit and update the project file.
The affected files will be added to the project, however, the dependency will not be preserved.