I am recording solo vocals using Cakewalk Sonar and a Cakewalk ua25EX on top of midi tracks. The UA25ex only records left or right depending on input (1 or 2). Regardless of the DAW's interleave button (stereo/mono), L/R channel-slider, I cannot get the vocal in the "center" of the mix. The monitors play the track with the vocal centered (track VU shows Left but Master shows vocal is both L/R   but when it's exported it defaults back to left channel only. I am not adding any effects directly, but adding reverb on a separate bus track (which ends up on the right channel only). I'm thinking I've got some setting wrong somewhere in the chain. Any thoughts? I'm using an older version of Sonar and (don't laugh too much) a Windows 7 computer. For the little home projects I do... it works!

Sounds like your vocal track in sonar is a stereo one. It should be a mono one.
All is not lost. You can convert your stereo vocal track to a mono one by (I think) right clicking on the track and selecting convert to mono.
 
This will allow you to then pan the vocal track as you wish.

Thank you.  I'll give that a go. Now my question is HOW can I just record in mono in the first place? Maybe it isn't possible using the Cakewalk ua25ex interface. The manual says input 1 is Left/ 2 is right. No option for mono.

Gleemor
...HOW can I just record in mono in the first place? Maybe it isn't possible using the Cakewalk ua25ex interface. The manual says input 1 is Left/ 2 is right. No option for mono.

 
It doesn't matter which input you use. Just set the track interleave to mono and it will record in mono.

Alas...That's where the problem lies. Regardless of whether the interleave is mono or stereo, the output when mixed is always one (left) channel. Prior to exporting the audio, the interleave is set to record/playback Vocals in mono but automatically reverts to left channel only upon export.
 
 
 
 
 

Is the recorded audio clip mono? Does it display a single waveform rather than a double one?

Shows a single waveform (left of stereo pair..Right side blank) regardless of interleave position during recording, but Master shows matching left/right levels. Monitors play vocal through both speakers until exporting audio. Then vocal is only on left side (no effects) and reverb (added on bus) only on right side at low volume regardless of fader position.

Gleemor
Shows a single waveform (left of stereo pair..Right side blank) regardless of interleave position during recording...

 
That's a double waveform, i.e. stereo. The recorded clip should be mono. Have you got some stereo fx in the track?

Zero FX on track. Not even EQ. Add all of that to bus-trak/mix. Found out some time ago that FX on armed audio track can be problematic.
 

Which version of Sonar? That might help narrow things down.