I agree with Chance, these appear to be fi and fl ligatures. If you're copying and pasting from another file that has special ligature characters typed in, I would just replace these with regular fi and fl characters. I believe that modern fonts will create a ligature automatically, if it exists in the font.
Thank you for your opinions! It turns out that it was indeed an error connected to the font type I was using. When I changed the font to another one, the issue has gone! Too bad that it's the company font we're supposed to use... :))
Thanks for helping!
