Lenses for Sony A55V
All Minolta, Konica-Minolta or Sony Autofocus (A-Mount) lenses will work on your camera. Tamron and Sigma A-Mount lenses will also mount although there have been some compatability problems with the camera's software with some older Sigma lenses. Haven't heard of a problem with an Tamron lenses.
If your Tamron lens won't mount I would suspect it was designed for either a different brand camera or the older manual focus Minolta mount.