It happened to me in the past. This may be more of a problem with Visual Studio than anything else.
This means that the AssemblyInfo.cs file is either missing from the Properties folder in the project, or there is a problem with access rights. If there is a problem with access rights, update the ACL (File> Properties> Security), close and reopen the project. If you are absent at all, you just need to recreate it by following these steps:
- In Visual Studio 2010, select Tools > Create GUID
- Click Copy (or New GUID , then Copy )
- Click Exit
- Expand the Properties folder in Solution Explorer ( Control + W + S to open)
- Delete AssemblyInfo.cs file shown with exclamation point
- Double click on the "Properties" folder - the "Properties" window will open
- On the Application tab, click the Application Information button
- Fill in the application information, paste the GUID that you copied into the GUID field - when done, click OK
Source : Visual Studio 2010 Project Error AssemblyInfo.cs failed to open
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