Carol:
I would have to look back at my research notes from the time I worked on
levamisole, but I'm fairly sure 1M is not soluble at room temperature or
below.  In addition, it degrades over time, and throws down a whitish
precipitate.  Again, in my research notes, I have the reference to an
analysis of this degradation, but as far as I remember, part of it is a
dimerization.  In any case, the products are not inhibitors of AlPase.
If you can get it into solution at 1M, so much the better, but don't
keep the stock around too long.  I don't know if it will freeze
successfully (which should reduce the rate of degradation), but
aliqotting the stock and storing it at -80° might help.  Otherwise, use
it as fresh as possible.
Good luck,
Adrian Leek.