Is there a problem to eat fish with cheese, or is it only a problem to eat fish with meat?
The Beit Yosef (Y.D. 87) wrote that one should not eat fish with cheese. However, many poskim (Taz, Shach, and others) wrote that this was a printer’s mistake, and he really meant to write “meat” and not “cheese”. On the other hand, there are many poskim (Lvush, Zivchei Tzedek, Kaf Hachaim) that hold that this was not a mistake, and the Beit Yosef indeed meant to forbid eating fish with cheese.
The prevalent custom among ashkenazim is to permit this, however among the sefardim many are stringent. Every person should follow their custom or consult their own rabbi.
See the poskim in Y.D. 87