>- DECLARE the function i want:
> DECLARE INTEGER OptelFuntie IN "D:\PROJECTS\DLLTEST\PROJECT1.DLL";
> INTEGER val1, INTEGER val2



> ln_Uitkomst = OptelFunctie(3,4)


You declare a function called OptelFuntie, but is calling OptelFunctie. If you copy/paste the declare code, then you are missing a c in the function name of the declare.

HTH,