I am sorry to hear about the issues you are experiencing.
Could you tell us if this error message is visible only in design time and you can run the project without throwing exception at runtime?
One of the possible reasons for seeing this error message could be the cache which is created by the Visual Studio, so you can try to:
1. clean and rebuild the project.
2. or delete manually the bin and obj folders then rebuild the project - this will ensure that all unnecessary files will be deleted.
If the issue is connected to the Visual Studio designer, you can also do the following:
1) close all visual studio instances.
2) go to C:\Users\<username>\AppData\Local\Microsoft\VisualStudio\<visual_studio_version,for_example_12.0>\Designer\ShadowCache and delete the folders there - this is the cache of VisualStudio's designer.
If none of this helps, we will need more detailed information to further investigate the reasons behind the behavior (e.g. the version of your Visual Studio, if you are using third party extensions for Visual Studio, etc.). Also it would be great if you could send us an isolated project where the issue appears. This will allow us to test it and further investigate the case.
I am looking forward to helping you solve this issue.
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