Add a note before the acciaccatura, because, in order to
understand the error (and the solution), you need to compare
the whole duration of the acciaccatura block with the duration
of the previous note. (Thanks Federico!)
duration, for example:
@example
-\acciaccatura @{ c'8[ d' e' f' g'] @}
+c'8 \acciaccatura @{ c'8[ d' e' f' g'] @}
@end example
becomes:
@example
-\acciaccatura @{ c'16[ d' e' f' g'] @}
+c'8 \acciaccatura @{ c'16[ d' e' f' g'] @}
@end example
Or explicitly change the musical duration:
@example
-\acciaccatura @{ \scaleDurations 1/2 @{ c'8[ d' e' f' g'] @} @}
+c'8 \acciaccatura @{ \scaleDurations 1/2 @{ c'8[ d' e' f' g'] @} @}
@end example
See @ref{Scaling durations}.