std::string manipulating error on C++Builder 6

I am creating a class for a project using an Emericc axe. The goal of this class is to use the error frames to return a message. I have to use only STL's std::string variables. However, the IDE doesn't recognize any string manipulation after one of the find functions.

Note that I'm French, so the variables I use are in my language (the code is pretty simple tho).

The error I encounter is in this function:

string ErrMericc::ErrTrame(string trame)
{
  /*
   trame(fr) = frame(eng)
   virgule(fr) = comma(eng) [I shortened "virgule" to "virg" in a variable]
  */

  this->trame=trame;
  trame.find('!', posExcl); //this marks the beginnig of the error number

  if(posExcl == string::npos)
  {
    trame.clear(); //clearing in case the variable is not empty
    //in case this is not an error frame
    trame.push_back("Erreur 200 : "+errors[200]+". La trame envoyée n'est pas une trame d'erreur."); 
    return trame; 
  }
  else
  {
    trame.find(',', posVirg); //here is the error
    //starting here, no function using a string is recognized by the IDE
    //and I don't find why
    nb.push_back(trame.substr(posExcl+2, posVirg)); //unrecognized push_back() and substr()

    errNb=StrToInt(trame.c_str());
    trame=errors[errNb];
    return "Erreur "+IntToStr(errNb)+" : "+trame;
  }

}

C++Builder 6 tells me : [C++ Error] ErrMericc.cpp(1): impossible to call code execution, because of source code errors. When I double click on this error message, it brings me at the first line of source code in the file.

The error message doesn't seem to stop popping except if I comment out the "trame.find(',', posVirg);".

Could you please explain me where my error is?

EDIT:

It looks like C++ Builder 6 just doesn't like the code line...

This works:

    trame.find(',', posVirg); //here is the error
    //starting here, no function using a string is recognized by the IDE
    //and I don't find why
    nb.push_back(trame.substr(posExcl+2, posVirg)); //unrecognized push_back() and substr()

This doesn't:

    //here is the error
    //starting here, no function using a string is recognized by the IDE
    //and I don't find why
    trame.find(',', posVirg); 
    nb.push_back(trame.substr(posExcl+2, posVirg)); //unrecognized push_back() and substr()

Weird.

I'm starting to think the problem comes from the IDE. So far, I've tried copying and moving the files into a new folder, but the malfunction isn't affected.

Turns out the error came from my using of the push_back() function : I can push back only one char at a time.
Inputing multiple values in one memory location, made to contain one char, wasn't a good idea.

Apparently, C++Builder 6 just didn't know what to do as the errors came from my use of something in the stl.

So I shouldn't have done :

trame.push_back("Erreur 200 : "+errors[200]+". La trame envoyée n'est pas une trame d'erreur.");

But :

trame = string("Erreur 200 : ") + errors[200] + string(". La trame envoyée n'est pas une trame d'erreur.");