My track changed keys and I'm not sure why.

I own the latest Sonar Artist. I am still learning all the in's and out's of this program. This is my first experience with a DAW, although I am no stranger to a soundboard both digital and analog.
I currently am working on a demo for myself as a singer. I am using prerecorded backing tracks and recording my vocals doing all necessary processing and bouncing the tracks. I have one track that I'm not sure exactly what happened but it now plays back about a half step down. It hasn't been bounced yet so it's still in multi-track form. I just would really like to figure out what I did, it's not really a big deal to re-record it, just want to figure out what I did so I know how to correct it in the future on more critical projects. 
Thanks
 

slartabartfast
It probably also plays slower as well, but that is more difficult to appreciate sometimes. This is the classic case of a data set with a 48 K sps sample rate playing back at 44.1 sps. As to why it is happening, that may be a little tricky. The first place to look is to see if some other application has re-set the sample rate on your audio interface driver. 

Thank's for your reply, you hit the nail on the head on this one. I am not sure what program changed the settings but I suspect Serato DJ. I haven't been able to duplicate it but at least now I know how to correct it.