The document contains errors that must be fixed
When you work with a XAML file in the WPF Designer for Visual Studio, Design view and XAML view are synchronized automatically. For more information, see Split View: Viewing the WPF Design Surface and XAML at the Same Time. If a XAML file contains a syntax error, Design view cannot be synchronized. This error can be displayed to the user in Design view or the Information bar.
Design View
If the file is closed and you open it, the following message appears in Design view of the WPF Designer:
Problem Loading
The document contains errors that must be fixed before the designer can be loaded. Reload the designer after you have fixed the errors.
Reload the designer
You must edit the XAML to correct the error, and then you can click Reload the designer to update the designer.
Information Bar
If the file is already open and a new error is introduced into the XAML, the following message appears in the Information bar of the WPF Designer:
The document contains errors that must be fixed before the designer can be updated. Click here to open the Error List.
You must edit the XAML to correct the error. Once the XAML is corrected, the designer updates automatically.
See Also
Concepts
Troubleshooting WPF and Silverlight Designer Load Failures
Other Resources
Debugging and Interpreting Errors in the WPF Designer