Question: MAPLE wont evaluate a matrix with an unknown

Hi,

I need to find the eigenvectors of this matrix and get the following error:

> eigenvects(A);
 linalg:-eigenvects called with arguments: [[200, -96, 5, -4.4, 4.7, -12.6, -6.2], [-96, 320, 33.1, 6.8, 4.5, 7.4, -.3], [5, 33.1, z, -51.1, .8, -8.4, 7.6], [-4.4, 6.8, -51.1, 110, -76.6, -14.2, -67], [4.7, 4.5, .8, -76.6, 270, 78.3, -.1], [-12.6, 7.4, -8.4, -14.2, 78.3, 420, 38.3], [-6.2, -.3, 7.6, -67, -.1, 38.3, 230]]
 #(linalg:-eigenvects,7): return linalg:-`eigenvect/float`(A)
Error, (in linalg:-eigenvects) matrix entries must all evaluate to float
 locals defined as: i = 3, j = 3, m = 7, n = 7, t = z, B = (array( 1 .. 7, 1 .. 7, [( 2, 4 ) = 6.8, ( 2, 6 ) = 7.4, ( 1, 6 ) = -12.6, ( 2, 3 ) = 33.1, ( 2, 7 ) = -.3, ( 2, 1 ) = -96., ( 2, 5 ) = 4.5, ( 1, 5 ) = 4.7, ( 3, 2 ) = 33.1, ( 1, 2 ) = -96., ( 1, 3 ) = 5., ( 1, 4 ) = -4.4, ( 1, 1 ) = 200., ( 2, 2 ) = 320., ( 1, 7 ) = -6.2, ( 3, 1 ) = 5. ] )), islist = islist

However, it works for, for example:

> G := [[1, 2, 3, 4, 5, 6, 7], [z, 2, 3, 4, 5, 6, 7], [x, 2, 3, 4, 5, 6, 7], [1, 2, 3, 4, 5, 6, 7], [1, 2, 3, 4, 5, 6, 7], [1, 2, 3, 4, 5, 6, 7], [1, 2, 3, 4, 5, 6, 7]];
   [[1, 2, 3, 4, 5, 6, 7], [z, 2, 3, 4, 5, 6, 7], [x, 2, 3, 4, 5, 6, 7],

     [1, 2, 3, 4, 5, 6, 7], [1, 2, 3, 4, 5, 6, 7], [1, 2, 3, 4, 5, 6, 7],

     [1, 2, 3, 4, 5, 6, 7]]
> eigenvects(G);
                             [                      (1/2)       ]  
         [0, 5, {, , , , }], [14 + (191 + 3 x + 2 z)     , 1, {}],

           [                      (1/2)       ]
           [14 - (191 + 3 x + 2 z)     , 1, {}]

sorry for the presentation....

So its not the fact that a 7 by 7 matrix with unknowns is too much for MAPLE to handle. Whats the problem and is there any way I can get around it???

Thanks very much for any help you can offer, getting this eigensystem is quite vital to my work!!!