Really?
So was Pope Stephen in error in doctrines of faith or morals when he had his predecessor exhumed and held to trial (while dead) for violations of cannon law and other charges - or was Pope Formosus in error in doctrines of faith or morals as Pope Stephen charged?
Hard to say that neither men erred in doctrines of faith or morals. One of then had to be wrong.
Pope St. Stephen served the church from 12 May, 254, until his death on 2 August, 257. Which pope did he exhume?