[Nauty] Error using nauty with more than 32 vertices?

[Nick Penwarden]

I'm calling nauty in my program to determine if two graphs are 
isomorphic. I am doing so by calling nauty once for each graph to get 
the canonical sum of the graphs and then comparing them with the 
testcanlab function. This works perfectly on graphs with <= 32 vertices, 
but does not work properly for graphs with > 32 vertices. Sometimes it 
segfaults and sometimes it just returns that the graphs are not 
isomorphic when they in fact are.

I have defined MAXN as 64, and am passing n and m correctly to both 
nauty and testcanlab. Any ideas?