Given that the past participle of "write" is "written" and the preterite is "wrote", the forms of "copywrite" should be "copywrote" and "copywritten", not "copywrited."
That seems logical, unfortunately the only response which can be made is "English is weird".
(Though people do try to generalise rules like this, I see a lot of foreigners try to write "payed" instead of "paid". Similar idea, and equally logical.)
