Scale_x_manual error (extra point on legend)

[Michael Caruso]

When I run this script I am receiving an error: 

ca1.gr=ggplot(ihc,aes(Latency,CA1.GR.ir, group=Arena))+

  geom_smooth(aes(fill=Arena, color=Arena),method="lm",se=FALSE,size=1)+

  geom_point(aes(shape=Arena, fill=Arena, color=Arena),size=3.5)+ # add a scatter plot; constant size, shape/fill depends on stress condition

  scale_x_continuous("Z-Score for Mean Latency to Approach Novelty (PND 70)",

                     limits=c(-3.5,3.5), 

                     breaks=seq(-3,3,by=1))+

   scale_y_continuous((expression(paste('Hippocampus CA1 GR+ cells /  ', mm^{2}))),

                     limits=c(5,10),

                     breaks=seq(5,10,by=1))+ 

  ggtitle('Figure 6a.')+

  scale_shape_manual(name="Exploration Arena",

                     breaks=c("Novel Physical", "Novel Social"),

                     labels=c("Novel Physical", "Novel Social"),

                     values=c(21, 24))+ # explicitly have fillable shapes for each group

  scale_fill_manual(name="Exploration Arena",

                    breaks=c("Novel Physical", "Novel Social"),

                    labels=c("Novel Physical", "Novel Social"),

                    values=c("red","black"))+

  scale_color_manual(name="Exploration Arena",

                     breaks=c("Novel Physical", "Novel Social"),

                     labels=c("Novel Physical", "Novel Social"),

                     values=c("red","black"))+

  theme_bw()+

  theme(plot.title = element_text(face="bold", size=24, vjust=2, hjust=-0.1), #use theme_get() to see available options

        axis.title.x = element_text(size=24, vjust=-0.5),

        axis.title.y = element_text(face="bold", size=24, vjust=1.0, angle=90),

        axis.text.x =  element_text(size=20),

        axis.text.y = element_text(size=20),

        panel.border = element_rect(size = 0.5, colour = "black"),

        panel.grid.major = element_blank(), # switch off major gridlines

        panel.grid.minor = element_blank(),

        legend.justification = c(1,1),

        legend.position = c(1,1), # manually position the legend (numbers being from 0,0 at bottom left of whole plot to 1,1 at top right)

        legend.title = element_text(face="bold", size=15), 

        legend.text = element_text(size=15),

        legend.key.size = unit(1.0, "lines"),

        legend.key = element_blank()) # switch off minor gridlines  

ca1.gr

Error message = 

Error: Insufficient values in manual scale. 3 needed but only 2 provided.

In addition: Warning messages:

1: Removed 17 rows containing missing values (stat_smooth). 

2: Removed 17 rows containing missing values (stat_smooth).

The additional warnings are ok because they don't affect my figure. However, the manual scale thinks I need 3 values when there are only two in the data set. Any idea why this is happening?

Thank you,

Mike