ghci doesn't run FFi'd code which works under ghc on WinXP

Hi All, I wrote a binding to matlab matrix.h and mat.h. My test program works when I compile a binary, but when I try to use the code in ghci nothing happens. There are no error messages, but all computations return a blank line. Does this fall into a known class of error? I can provide my source code, but because of licensing requirements I can't provide the .dll's against which the code is linked. TIA Vivian