In one case I copied and pasted previous working "packaged_resources"
in the bin folder.[the problem was it did not reflect the UI changes]
Other I opened the visual studio as
administrator.
Next changed the "Minimum target to Android" to lower
apis in the project properties windows.
I suggest not touching the code behind of the design. If you get this error simply pull some button from the tool bar into the design and visual studio will come to its consciousness that there is change in UI. Next click on save all so that it make necessary change in the designer file.