What do you mean with "When i try to add new field it just removes it"?
If it happens in the <b>content class</b> than it is a bug
Remember that you have to create a new object to reflect new fields as information collectors from the content class, so delete the old one (also from trash to avoid funny url alias) and re-create it
Well I tried to add a from in an article mean 1st i created an article and then in its content i wrote form and its fields code and it did not worked, It said unsuspacted tag input has been removed.
What if i don't create artcile and go for some other thing, will it support creating form?