What is it? Why is it a problem?
Also see these links: 10 dangers of theistic evolution Did the Creator use evolution? Some Questions for Theistic Evolutionists and Progressive Creationists
From Bert Thompson, Ph.D's book titled "Christian Evidences", pages 89 - 90:
The word "theistic" comes from the Greek word theos, meaning God. Therefore, when one claims to be a "theistic" evolutionist, he is claiming to believe in both God and evolution at the same time. As Dr. J. D. Bales has remarked: "There are many in the religious world, and a few in the New Testament church, who think that Genesis can and must be harmonized with evolution. They are theistic evolutionists who maintain that evolution was God's method of creation" ("Theistic Evolution & Genesis, ", IN: Gospel Advocate, January 24, 1974, p 52). Dr. R. L. Wysong, in his book, The Creation-Evolution Controversy, has observed, "Basically, theistic evolution contends that abiogenesis (the spontaneous formation of life from chemicals) and evolution (amoeba to many through eons) have occurred, but a creator was instrumental in forming the initial matter and laws, and more or less guided the whole process" (Inquiry Press, East Lansing, Michigan, 1976, p 63).
The point is clear. The theistic evolutionist believes organic evolution was simply "the way God did it" as He brought the Universe and its contents into existence. And although there are almost as many varieties of theistic evolution as there are people who espouse it, a few characteristics are common to all. For example, the theistic evolutionist believes in: (a) an old Earth; (b) wholly natural processes responsible for life as we see it, once the initial matter was brought into existence by God, and; (c) a figurative (non-literal) interpretation of the Genesis account of creation.