Rather coincidentally one of my colleagues created a solution in the last day or two on exactly the same problem.
The Lint problem has been fixed in IC616, however, if you turn on the "Performance" switch on the SKILL Lint form, you'll get an output like this:
HINT (LAMBDA1): ~/skill/forum.il, line 9 (bug) : lambda and nlambda statements do not need to be quoted : 'lambda((s1 s2) let((b1 b2) (b1 = (\& \& \&)) (b2 = (\& \& \&)) ...))
The solution is to remove the ' before the lambda. It's not necessary, and without this SKILL Lint won't fail with the BADRULE error.