Random crashes when calling functions from a dll

I am experiencing crashes of Matlab when I call functions from an external dll (with calllib). What is especially weird is that all of these functions causing crashes actually work... from time to time. When I run my script containing the calls to functions, it can crash at one point, then I run Matlab again, run the script with the exact same input data, and it crashes at another function call, or even between function calls! There is no obvious crash pattern.

I cannot attach the dll itself but here are the header file and the script containing the calllibs, if it is of any help.

[Arnaud Samie]

I forgot the crashlogs, here are a few of them...

[Arnaud Samie]

And here is some debug info from Visual Studio... Looks like it comes from Matlab more than the dll

[Charles Smith]

Did you ever find a solution to this? I'm having a similar issue.