An error occurred creating the form

I can't find where is the problem, because i don't know in which line is the error. Only know that is before form_load event. Currently I don't know what to do and where to put break point, please help.

When i start the application error is raised without line marker:
An error occurred creating the form. See Exception.InnerException for details. The error is: Object reference not set to an instance of an object.