Unable to edit New form if fields/Columns are more than 60 or 65

I am facing very unusual problem which is I am not able to eidit NewForm if fields/Columns are more are more than 60 or 65.

http://ift.tt/1FQVqan

By following above link I have added TestNewForm.aspx and trying to edit but I getting very stupid and unclear error message like this

Unable to display this Web Part. To troubleshoot the problem, open this Web page in a Microsoft SharePoint Foundation-compatible HTML editor such as Microsoft SharePoint Designer. If the problem persists, contact your Web server administrator.