If you are trying to load a windows smart device project set to .Net CF v3.5 in Visual Studio 2005, you might get this error message:
the project could not be opened because it refers to a device plaform that does not exist in your datastore
The reason being VS 2005 cannot work with .NET CF v3.5.
The workaround is to set project file’s .NET CF target framework to v2.0. i.e.
<TargetFrameworkVersion>v2.0</TargetFrameworkVersion>
Sources: