I must admit, that I'm not even an amateur in Programming in LabView. I even dont know how to use those error in/outputs...Thanks eveyone for the advises and further links and literature. I try to study them by time.
The problem is finally solved. In my opinion the main reason is that LabView Checks the DLL before they are compiled.(?)
So if there is a portion of somehow inconsistent code in Function a...then the complete function_a is omitted !!! (Altough it was good enough for Vi its not worth for the exe)
And indeed i found some suspecious Code in the function_a.. Was able to rearrange it and voila it Works.
So if anyone focus this problem....Check first the c++ or .net code you wrote. 😉