I'm still struggling with this.  I realise taking such a determinant will use a lot of memory, but I have 16GB and currently maple is only using up to 800MB before giving the error.  There must be a way of telling maple to use more memory????

And Axel, thanks for the help but LinearSolve is no use to me in this case, I need to take the determinant.

Thanks you folks, I ended up using Markiyans method (works great, thanks), but my thanks to all of you.

~ 90% of the elements are zero, the others are simple expressions like q*B, 1/2 * m/c, etc where the letters are just undefined constants. I never defined explicitly what type the elements are. The way I generated the matrix was to take my system of linear equations - contained in a set 47 elements long - and use the

Mat,b:= GenerateMatrix(system, variables):

command to generate my matrix Mat.

Oddly if I take a subset of the matrix (e.g I form a 40x40 matrix out of the first 40 rows and 40 columns of the one I'm interested in) maple can calculate the determinant (and does so almost instantaneously), however when trying to do the same for the full matrix I get the above error. This leads me to think its not a memory issue at all, but rather a bug of some sort.