Yes, that occurs if you have a

using namespace std;

statement in your code, and you are using Microsoft Visual C++ 6 (it's actually a compiler bug).

Removing (or possibly moving until after all your includes, or just re-ordering your includes) the using statement will fix the issue.

Thanks very much for that hint John, I found two places in our header which are using the "using namespace std;". After I have switched that to the explicit "using" statements I could also switch back to your default "user.hpp". Perhaps I can ask one more question about this strange behaviour, just because I want to understand why: I try to use my own string class, which is inherited from std::string. Defining "VC6_STUPID_BEHAVIOUR" in the example code below compile and run the code successfuly, using the expanded name leads to following compiler error: error C2614: 'MyCString' : illegal member initialization: 'string' is not a base or member You know WHY??? Also because of the same compiler error in VC6 or is there something else wrong. On Solaris and HP-UX it works fine in every combination. // vvvvvvvvvvvvvvv snipp vvvvvvvvvvvvvvvv #include <string> #include <iostream> #ifdef VC6_STUPID_BEHAVIOUR using std::string; # define std_string string #else # define std_string std::string #endif class MyCString : public std_string { public: MyCString(const char *s_); : std_string(s_) { std::cout << "\"" << *this << "\"" << std::endl; }; }; int main (int argc, char *argv[]) { MyCString s(argv[0]); return 0; } // ^^^^^^^^^^^^ snipp ^^^^^^^^^^^^