An Invitation letter is a simple letter written to invite or request the presence of an individual or groups of patrons for a celebration or an important function. It can be an informal or formal...
A business letter is to communicate business matters; none of the business letter is a personal letter. Even if you know the person the letter is for very well, keep a business letter on a business...
Dear all while thank you very much for your invitation would like to bring to your kind attention that, as I am too busy at present being cann't take part at this time. thank you again best regards,