AFL - non-sublicenseable versus distributable

[seterajunk at charter.net]

Hello,

I have an open source project currently licensed under the AFL version
1.2.  I've recently received some interest from a corporation that would
like to use my project, but they are concerned with the non-sublicenseable
statement in the license.  Their lawyers feel that the distributable terms
might cover them, but that they usually consider that a sublicense.

Can anyone explain to me what the term sublicense really means and what I
would be giving up by allowing this company to sublicense my code?  The
fact that it is called out as non-sublicenseable makes me hesitant to
allow sublicense without further understanding the implications.

Thanks,
Craig