One of the more annoying bugs in 1.6.x is that multi-prim objects will spontaneously de-link. Then upon trying to re-link them, the "Link failed -- pieces too far apart" message appears. I've had this happen many times now, and I can promise that in each case, the pieces were nopt actually too far apart. Just now for example, it happened with a chair, a frickin' 1.5 meter chair for god's sake. No way are 4 chair legs, a seat, and a back "too far apart".
Anyway, after spending many frustrating hours trying to figure out how to get things to link properly, in some cases just rebuilding altogether, I finally stumbled upon a simple solution. Select all the prims in question, and shift-drag to duplicate. Once the duplicartes appear, delete the ones you are dragging (the originals), and then work with the duplicates (the ones that stayed in place). These newly created prims will function normally. Halleluyah!
Unfortunately there seems to be no way to predict or prevent the de-linking poltergheist from rearing its ugly head, but at least the damage can be undone. The problem has now gone from devestating to just annoying.