Compiler doesn't build after simple modification

I'm sorry if my question is very stupid or very basic but I'm not so confident with building process. So this is the problem. I wrote a c++ project, I compiled it and was working perfectly on Code::Blocks 17.12 with version C++11. I sent the project as it was to a friend of mine, he opened it (older version of Code::Blocks like 16.something) compiled it and it was working as in my pc, then he made some modification, but stupid ones (even deleting a ';' and the adding it immediately or adding a space ' ' somewhere) but after this the compiler started giving errors like:

error: 'class myclass<std::__cxx11::basic_string<char> >' has no member named 'clear_data'

when actually the class has it and before calling that function I called lot of others from the same class defined exactly the same but having no errors.

So he decided to copy the code, class by class, in another project, creating everything from zero and the code started to work again allowing modifications. He sent the project back to me and got the same problem!!! How can I solve this?