I guess you are trying to do (simplified example):
\score {
\new ChoirStaff <<
\new Staff { c'1 }
\new Staff { c'1 }
>>
\new ChoirStaff <<
\new Staff { c'1 }
\new Staff { c'1 }
>>
}
That's not what LilyPond expects. In a \score block,
there must be one music expression, hence the warning
"spurious expression in \score". Please see
https://lilypond.org/doc/v2.22/Documentation/learning/score-is-a-_0028single_0029-compound-musical-expression
The problem is that there are several of them here,
and you are not telling LilyPond how to group them.
They have to be in parallel, not one after the other,
so they should be surrounded by << >>.
\score {
<<
\new ChoirStaff <<
\new Staff { c'1 }
\new Staff { c'1 }
>>
\new ChoirStaff <<
\new Staff { c'1 }
\new Staff { c'1 }
>>
>>
}
This gives the default grouping, documented at
https://lilypond.org/doc/v2.22/Documentation/notation/displaying-staves.html#grouping-staves
Namely, a mere bar to group the staves, and
no connected bar lines. That is exactly what
you want here.
To elaborate: \new GrandStaff does not necessarily
call for << >> even if that is typically what you
want to feed it. The syntax is \new GrandStaff xxx
where xxx is any music expression. You could just as
well say
\new GrandStaff {
<<
{ c'1 }
{ c'1 }
>>
<<
{ d'1 }
{ d'1 }
>>
}
even if that does not make a lot of sense
musically.
Only the first system is rendered.
The second solution leads to the same result/error message.
While I admit that the Grandstaff-option leads to undesirable spanned
barlines, in version 2.19.82 it performed the wanted grouping,
without the extra brace seen in 2.23...
This change was intended. What's happening in 2.22 and
earlier is that GrandStaff does not accept ChoirStaff, so
the GrandStaff actually does not receive any music at all
and ChoirStaff contexts are inserted inside Score. This
has the consequence that the expected brace is not
inserted. There are a number of similar cases. They
were sorted out in the development series by this
change in the LilyPond sources:
commit e31b0b75a9a7b6e01ecd9c9a05dc3108a89273be
Author: Jean Abou Samra <jean@abou-samra.fr>
Date: Sat Apr 17 11:48:58 2021 +0200
Derive all StaffGroup-like contexts from StaffGroup
Previously, there were many inconsistencies between the context types
StaffGroup, ChoirStaff, GrandStaff and PianoStaff. They had
differences
in their lists of accepted contexts, and setting localAlterations
or not.
This lets ChoirStaff and GrandStaff inherit from StaffGroup
(PianoStaff
still inherits from GrandStaff) to keep all of them in sync.
StaffGroup gains a bunch of \accepts, so it accepts everything also
accepted by Score.
This fixes a problem occurring when a TabStaff was included in a
ChoirStaff.
The latter did not accept it, causing a StaffGroup to be inserted
in between,
with its own bracket.
Closes: #6094
In summary: your score was relying on buggy behavior.
Fortunately, it's easy to fix it by using the method
that is documented to give the behavior you want.
Hope that helps,
Jean