AssemblyInfo.cs' could not be opened ('Unspecified error ')

Error AssemblyInfo.cs could not be opened

So you open a project in Visual Studio 2010 and get an odd error:

AssemblyInfo.cs' could not be opened ('Unspecified error ')

What this means is that the AssemblyInfo.cs file is either missing from the Properties folder in the project or there is a permissions issue. If permissions, update the ACL (File > Properties > Security), close and re-open the project. If missing altogether, you just need to recreate it using the following steps:

1. Within Visual Studio 2010, select Tools > Create GUID
2. Click Copy (or New GUID then Copy)
3. Click Exit
4. Expand the Properties folder in the Solution Explorer (Control + W, S to open)
5. Delete the AssemblyInfo.cs file shown with the exclaimation point
6. Double click on the Properties folder - this should open the Properties window
7. On the Application Tab, click the Application Information... button
8. Fill in the application information, paste the GUID you copied into the GUID field - when done click OK