EZoto wrote (2003-09-14 19:00:30 PST):

[Fischer and Karpov] were close to agreeing
to a match until fischer said that the match
should be Fischer as World Champion and Karpov
the challenger. Karpov disagreed since he beat
korchnoi and was named champion. ... Karpov
said no and Fischer said I'm not playing then.

_
This is not the version of the story that I
have heard. Here, for example, is a version
that Larry Parr said that he received in an
email:

"I'm sure you've heard the famous Campo
story, about Fischer and Karpov staying
at different hotels in D.C., with Campo
as the intermediary, running between the
two with a contract for the World
Championship. Each page laboriously
initialed by both, with Karpov agreeing
to all the asinine demands - until they
got to the final stage. When it came to
the final signatures, Fischer decided to
change 'Fide World Championship' to
'Professional World hampionship.' Karpov
-- or his Russian 'advisors' refused to
accept the change to a page already
initialed."

This, it should be noted, would have been AFTER
the events in 1975 when Fischer refused to
play without his 9-9 condition.

"Bobby Fischer had sent in a number of demands ... Some
of these were conceded ... But two demands were rejected.
... Numerous telegrams had been sent to the Congress by
Fischer via his spokesman, Fred Cramer. The last one said
that, in the light of FIDE's decisions, he was resigning his
FIDE world-championship title. ... Another attempt was
made to bring the FIDE and Fischer into complete accord,
when Colonel Edmondson (U.S. Chess Federation) asked
for the summoning of an extraordinary meeting of the FIDE
Congress. There being a sufficient number of countries in
agreement, it duly assembled at Bergen-aan-Zee in the
Netherlands from 18 to 20 March, 1975. It was an
extraordinary congress in every sense of the word, and
eventually, after much heated discussion, one of Fischer's
demands was conceded: the match was to have a limitless
number of games. But Fischer's other demand - that a
draw be declared when the situation reached nine to nine
- was rejected by a majority of three. Fischer's words on
hearing this were, 'It's all over then.' No match took place.
Fischer ignored the request to say by 2 April whether or not
he would play, and Karpov became the new world champion"
- Golombek (1976)