I think we need to know whether you're talking a little blurred or very blurred - if you can read the reg with an unaided eye on the orginal, can you read it on the resulting scan?
If no, then I think we're looking at a problem in the slide loading mechanism. Uneconomical to repair.
On the PhotoSmart, the lens is fixed focus and relies on depth of field to ensure focus. If your slide mounts are abnormally thick or thin, this might cause a problem, likewise would distinct film curvature. You could try scanning the slide upsidedown which might help bring the emulsion into focus - you can then correct in Photoshop or similar.
Colin K. Work, Pixstel