Tired of searching you project for that string? The answer is simple, which was proposed by Vladmir from Serbia on MSDN. The name of your class or form shares it’s name with a function or subroutine contained within that class. Like below:
public class Form1
private sub Form1()
…
end sub
end class
Changing the name of the method will fix this issue.
Refactoring Self 
[…] VB.Net C# Designtime Error ~ ‘.ctor’ is not a valid … – VB.Net C# Designtime Error ~ ‘.ctor’ is not a valid identifier. March 1, 2012 Tired of searching you project for that string? The answer is simple, which was proposed by Vladmir from Serbia on MSDN. […]