My project plays a half note higher than supposed to

[Jukka Riitaluoma]

I imported an old project of mine and re-worked it a bit. Everything was fine. Today I tried to continue my work, but now that project plays a half note higher than it supposed to play. What's wrong?

[John Vere]

This sounds like your audio system is set at a different sample rate than the project. 
 

Edited April 20 by John Vere