I've been having issues lately with dropouts and files playing back like they are speeding up and slowing down, and think I've finally figured out why, but can't fix it.  Although my interface's clock is set to internal, SONAR keeps switching its clock to Audio. I've checked several projects and it keeps happening to all.

Internal is for MIDI only projects. If there is audio in the project, the clock will switch to Audio.

I thought Audio was for incoming spdif.

I guess my problem is something else, although the speeding up and slowing down to me indicates a clocking issue.
 

Do you have the latest UX8 drivers that were released in May?

I do!

'Internal' is the PC system clock; as Steve said it's useable only for pure MIDI projects using direct-monitored hardware synths. 'Audio' is the interface's sample clock, and is required for any audio coming out of the box, including the audio metronome.
 
Check your Playback and Record timing Master assignments and/or try changing driver modes. You might also try renaming AUD.INI and letting SONAR build a new one on startup.

Playback and recording masters are set to inputs 1-2, as always. I will try renaming AUD.INI. Thanks, Brundlefly!

Didn't help. The problem is with a specific file that seems to have some internal problem or corruption. Other files work fine. The clock thing threw me for a loop thinking it could be my system.