Need help with Err. 27.

[animaedclxvi]

I got my Famicom replaced recently and began playing my FDS. I have spent the past few hours gunning through Castlevania, which ended on a rather disappointing note. To my dismay, I finally beat Dracula only to receive an Err. 27 message when flipping the disk to view the credits. After a few minutes of playing with the disk, I decided to try beating him again and still I got an Err. 27. The only other time I received an Err. 27 before this was periodically when starting up the game file. However, it worked when I inserted the disk again. Does anyone know why this only happens when loading the credits and not anywhere else? Is it the disk or the system? Please help, I really want to see the ending!

[80sFREAK]

ERR 27 is CRC error. There is probably some dirt on the surface or(bad scenario) damage. Try to clean surface very gently with cotton stick and IPA.