problem with ward 's linkage

hi,

I used this code two files , the code is running with one file and with other file turn out this

Warning: ward's linkage specified with non-Euclidean dissimilarity matrix. 
> In linkage at 178
  In ward_movielens1 at 7

ans =

       0

p=pdist(x,'euclidean');

   No_cluster=5;

   L=linkage(p,'ward');

   T = cluster(L,'maxclust',5);

thanks in advance