Ok, so I linked statically (to do that I only defined SFML_STATIC, is that correct?).
It did not fix the problem, but it made it occur on the beginning on the program, when I create an object of TtfText (in the closing bracket '}'. VS takes me to an _ASSERTE instruction in dbheap.c) .
So naturally I try everything that comes to mind, including eliminating the passage of sf::String in the constructor. Now the problem occurs when I exit the program (VS also takes me to the same instruction, I think).
Next thing I try is eliminating sf::Text completely in TtfText. The problem is now completely gone. If I keep the passage of sf::String in the constructor of the TtfText, the problem still happens when I exit the program.
Any ideas? It seems to be a problem with either sf::String, or sf::Text, or both. I hope the information I brought is helpful.
EDIT: Release version works perfectly.
EDIT2: Release statically linked comes up with the same errors that Debug statically linked, wtf.
I still don't know if I'm correctly setting it up for static compiling. Apparently not, since I get messages that I need the Dlls when I run the .exe withough the dlls in the folder.