error while calculating the eigen values

i was trying to calculate the eigen values of a matrix "a-K*c" but the error that i faced is-"Subscript indices must either be real positive integers or logicals."

where

a=1.0e004*[2.3020         0         0    0.6348
                0    0.5742         0    1.8741
                0         0   -1.9602   -1.8741
           3.4847    2.5659    8.7594   -0.0446]

K= 1.0e004*[4.8140    1.3309   -1.1422
            1.3309    2.7639   -0.8294
            -1.1422   -0.8294    0.3811
             3.2187    1.8474   -0.9689]

c=[1     0     0     0
   0     1     0     0
   0     0     1     0]

[the cyclist]

All you've shown us is the definition of the variables. Can you show the code that actually gives the error, so that we can reproduce it?