Using a guile extension written in c from mpb

Hi,
I've written some functions in c which can be called from guile 1.8. I
wish to use them in a mpb script, however I get segmentation faults
when I try this. I have compiled libctl and mpb with the same guile
library as my c functions. Any ideas what the problem might be, or
better suggestions on calling c functions from mpb?

Thanks for any help,
John Travers