I checked on the Internet and it seems that there are some special characters (sometimes also invisible characters) that produce this output, however I am not able to find and replace them. So I tried to use the utf8x option in inputenc, but now I get these 5 errors:
looreenzoo wrote:[…] P.S. This is my preamble: […]
The preamble alone is absolutely useless. For specific help it will require a complete but minimal example. Make sure that input encoding (UTF-8 here) and the encoding of the saved *.tex file accord.
While preparing the minimal example, I found out the problem, which was not in the .tex file, but in the .bib one. Since the errors were reproducible even without any text, I checked my references and there was an almost invisible sign upon one author's name. I canceled it, compiled the file, and got the same errors. So I cut the \printbibliography command, compiled the file, re-pasted the command, compiled again and now everything works.
Thanks for indirectly helping!