Sitecore Page Editor - An error ocurred when adding new control to placeholder.

Do you have problem to Add control to bottom of any placeholder in sitecore page editors  in sitecore Version 6.4.1 ?

Are you getting following error.

After spending an hour,  sitecore doesn't help much though.

Just did some debugging using dot peek find out that place holder names are case sensitive.

It will throw an error If place holder name is "Main" not "main" or "/contentArea/Right" not "/contentarea/right"

So make sure when you add control using content editor use all place holder name in lowercase and full path possible. else you could face above error.

It will throw above error.