The error comes from

(%i1) sm : sum(1/x - 1/(x+1), x, 1, inf)$

(%i2) sm, simpsum;

Sum is divergent

-- an error. To debug this try debugmode(true);

The simplify_sum in cvs computes the sum correctly.

(%i3) simplify_sum(sm);

(%o3) 1

(%i4) build_info();

Maxima version: 5.16post

Maxima build date: 10:20 11/12/2008

host type: i386-apple-darwin9.5.0

lisp-implementation-type: CMU Common Lisp

lisp-implementation-version: Stage 3 20071107T024924 (19D)

Andrej