When i try to remove my iCloud i get that my password is incorrect

Hello

When i try to remove icloud account (Find my iPhone) i get the error message Your Apple ID or password is incorrect or sometimes nothing sometimes just keeps asking for the password and the password it's OK because when i try on the browser and when i try to a other iPhone it works perfect but only on this one no it's iPhone 4S and i have IOS 8.3 i have reset network / settings / location i have check for the date and time but nothing fixed my problem so please help me.

Thanks