I tried ispell on the command line, and did get an error for 'nis2002':

% ispell -a
@(#) International Ispell Version 3.1.20 10/10/95
@nis2002

Word 'nis2002' contains illegal characters
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Since this isn't the behavior you're getting, perhaps you have two versions of ispell installed. It could be that the one you get from the command line allows 'nis2002', but the one that Text::Ispell is wrapped around doesn't.

One quick solution is to remove the numbers, and add just 'nis':

% ispell -a
@(#) International Ispell Version 3.1.20 10/10/95
nis2002
& nis 18 0: Dis, his, ins, is, n's, NBS, NFS, nib, nibs, NIH, nil, nip
+, nips, nit, nix, NTIS, sis, vis

@nis
nis2002
*
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BTW, I noticed on CPAN that Text::Ispell has been replaced by Lingua::Ispell. I don't know if the new module will fix your problem, but it shouldn't hurt.