How does one determine error?
Scriptural discernment through the Holy Spirit.
1 Corinthians 2:14 But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned.
Through prayerful study of scripture, one can know the truth.
Matthew 4:4 But he answered and said, It is written, Man shall not live by bread alone, but by every word that proceedeth out of the mouth of God.
2 Timothy 3:16-17 All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: That the man of God may be perfect, thoroughly furnished unto all good works.
The church.
Matthew 24:14 And this gospel of the kingdom shall be preached in all the world for a witness unto all nations; and then shall the end come.
Matthew 28:19-20 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you alway, even unto the end of the world. Amen.
Acts 20:28 Take heed therefore unto yourselves, and to all the flock, over the which the Holy Ghost hath made you overseers, to feed the church of God, which he hath purchased with his own blood.
James 5:14 Is any sick among you? let him call for the elders of the church; and let them pray over him, anointing him with oil in the name of the Lord
Hebrews 10:25 Not forsaking the assembling of ourselves together, as the manner of some is; but exhorting one another: and so much the more, as ye see the day approaching.
Jesus addressed issues in the seven churches in Revelation 1:1-3. He said that any church that remained unrepentant would have its candlestick removed.
Revelation 2:5 Remember therefore from whence thou art fallen, and repent, and do the first works; or else I will come unto thee quickly, and will remove thy candlestick out of his place, except thou repent.
What assurances do I have that my denomination is not in error? I prayerfully study scripture and rely on the Holy Spirit for discernment. I wouldn't remain in a church if I thought it was in error. In fact, when I came back to Christianity, I vetted every point, and I continue to do so as a member of the church.
In closing, let's revisit the questions presented.
Q: If the Bible alone is sufficient for a rule of faith, of what use is the SDA? Are they not a group of men and women apart from scripture and therefore subject to error? If we are to believe the Bible and the SDA, does that not make the claim of scripture only a slogan rather than a belief?
This would apply to the whole of Protestantism, not just SDA.
Protestantism: A branch of Christianity that emerged from the Reformation and emphasizes "sola scriptura," or the belief that the Bible is the only source of spiritual authority.
Protestantism is a major branch of Christianity that began with the Protestant Reformation in the 16th century when Martin Luther and others challenged the authority and practices of the Roman Catholic Church. Key Protestant beliefs include the Bible as the ultimate authority (Sola Scriptura), salvation by faith and grace alone, and only two sacraments (baptism and Communion). It encompasses many diverse denominations, like Lutherans, Methodists, and Baptists, and emphasizes the importance of the individual's relationship with God.