 I think this means an unequal sample in different conditions. But it seems
to mean something else. . .

I have a data set like below

particip    group   device  width   length  accep   thresh  rating
d-rating1           RA      Dingo   nom     nom     Y       5       8
     31           RA      Dingo   nom     long    Y       4       6
   21           RA      Dingo   fat     nom     Y       4       6
 21           RA      Dingo   fat     long    N       6       4
-2

and I'm running an ANOVA on it like so

aov.AMIDS_d <- aov(d.rating ~ group*device*width*length +
Error(particip/(device*width*length))+group,data.AMIDS_d)

This works ok until I try to print the condition means like so

print(model.tables(aov.AMIDS_d,"means"),digits=3)

and it says

Error in model.tables.aovlist(aov.AMIDS_d, "means") : design is
unbalanced so cannot proceed

According to the design, it ought to be balanced, so I need to check my
data structure. I tried

table(data.AMIDS_d[,2:5])

to give a table of observations per condition and got this

, , width = fat, length = long

     devicegroup Dingo SNAR
   NR    12   12
   NV    12   12
   RA    12   12
, , width = nom, length = long

     devicegroup Dingo SNAR
   NR    12   12
   NV    12   12
   RA    12   12
, , width = fat, length = nom

     devicegroup Dingo SNAR
   NR    12   12
   NV    12   12
   RA    12   12
, , width = nom, length = nom

     devicegroup Dingo SNAR
   NR    12   12
   NV    12   12
   RA    12   12

which looks both correct and balanced. So what am I missing, where's this
error coming from?

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