"Unknown option specified with the generic function of S-function" error when running MEX file in simulink

Hi,

I've received some files from another user but can't get the simulink model to run.

The problem is in an s-function block which calls a MEXW32 file. I DON'T have the source file, just the mex.

When I attempt to run the model (or even the block on its own) the error

"Unknown option specified with the generic function of S-function 'model_sf' in 'model_sfcn' "

the same number of times as the number of inputs + outputs, where model_sf is the name of the mex file and model_sfcn is the name of the s-function block.

There are three different s-function blocks in the model (none of which have source files), all of which give the same errors, again the same number of times as inputs + outputs.

Is this a problem only solvable by editing the source file? Or does the source file need to be in the directory anyway for it all to run?

Thanks in advance

Henry