Was working on a project and exporting wav versions of it.  Working fine.  Suddenly the wavs are all playing at what seems to be about half speed.  Tried an mp3 and got the same slow playback.  I don't think I changed anything, at least I didn't try to.  I'm sure there's a simple explanation... what is it?

Are they playing at half speed AND lower pitch or just half speed? Are they recorded audio tracks or MIDI driven synths?

Lower pitch as well.

And they are all MIDI driven synths.

Lower speed and lower pitch is usually a symptom of sample rate mismatch. Half speed would indicate something like 96K/48K. Check that the sample rate setting in your interface matches the Sonar project sample rate. Sometimes other programs that have access to the audio interface will change the sample rate there, even though you did not intentionally do anything. 

Turned out a reboot solved it.  Which should always be done before asking for help.  Sorry...

I had a recent issue on export where all the midi instruments were out of time with the audio tracks. Pitch was right but all the timing was out. Never really got to the bottom of it - one day it was fine, next day it was screwed, next day it was fine! Good luck!