Hi, EnsNentill! Welcome to the "Gotmead" community!!
Let me take a stab at answering your question. While it is often possible to make mead using crystallized honey with no ill effects, sometimes, especially if the honey has been in a crystallized state for a long time or if it has been stored in less than sanitary conditions, the liquid that remains in-between the crystals of solid sugar when honey crystallizes is at a specific gravity low enough that it supports the growth of spoilage organisms. So you can occasionally get a bad batch of mead when using honey that has been crystallized.
You may ask if you can taste the honey before committing to buying a large amount. You can also treat your must with metabisulfite immediately after dissolving the honey in water, to minimize the chances that a spoilage organism can get a foothold in there. If you do treat with sulfites, then allow some time (24 to 48 hrs) before pitching yeast for the sulfite level to drop to the point where it won't be a problem for the yeast that you pitch.
Oh, and Sasper's right - boiling, although a regular instruction in old mead recipes, is really not a good idea since it will drive off flavor and aroma elements of the honey. Better to heat your honey to a relatively low temperature (100 to 110 F is the rule of thumb that I use), and wait until it re-liquifies. It will eventually turn liquid again, if kept moderately warm.