How to include an auto generated file in a MsBuild project?

Question

Using MsBuild 4.0 I included a pre-build event that generates one of the project source files. But it seeks for the file before it is generated:

error CS1504: Source file 'c:\src\Data\Main.Designer.cs' could not be opened ('Unspecified error ')

The file is generated by DbMetal/SqlMetal. Is there any way to make this work?