I have gotten them to work sometimes and other times a dialog says they are unavailable.

I don't know what I am 'not' doing when I get the 'unavailable' dialog.

Typically just linking two layers together and using the tools. Last time around with two layers linked H/V tool worked fine. Then added a third layer and linked 2 and 3 and the tools would not work. Linked 1, 2 and 3 and they worked again. Should this be telling me something?

I am not sure what you are linking from what you describe. I imagine you are including the background layer in that linking? If so, you will get the error you mention when:

The background is linked to another layer, and is the active layer when you click the alignment tool.

The idea is, I guess, that the background can't be aligned to another layer if it is locked...that is, the background is always locked, so it won't move -- ergo the error.

I would imagine any time you align to the background when the background is not the active layer, you will get this error. Try making the background active, or turn it into a layer.

OK?

I'll bet that is what was going on - that I had the background layer involved in the 'aligning' process.

So many things to keep an 'eye' on - :-)

Thank you