I'm trying to convert a batch of my old .wrk files (from 2001 or 2) to .cwp files with X3. 
The first file was no problem, I just had to add a MIDI instrument, adjust some of the playback settings, and alter the MIDI buffer and it played back fine - no problem saving it either. 
However when I tried to do the same thing to my next file I ran into trouble.  For some reason when I try to play back the file, it plays the whole thing with a sort of an uneven swing feel.  I checked the quantizing and the notes themselves in the piano roll and everything is snapped to the grid for a straight feel.  Then I tried opening other projects, and found I had the same problem with all of them, even the ones that weren't written in eighth notes.
I've looked at several pages in the help literature, but none of them seem to address this issue.  Do any of you have any idea what might be going on? Any advice would be greatly appreciated.  Thanks!

I had some time to do some more experimentation to try and figure out my problem.
It seems that it may have something to do with tempo.  I examined one of my projects that played back correctly alongside one that didn't and noted that the first was set to 150bpm and the second to 170bpm.  By altering the second track's bpm to 150, it too was able to be played bacl correctly, albeit at the wrong tempo.  Curiously though, I have another project with a bpm of only 140 that plays back incorrectly.  However I could make it play back with an even feel by lowering the bpm as well.  As far as I can tell, every track I have will play back evenly at 100bpm, and the higher I go above that, the more tracks will start playing back with an uneven feel. 
I thought it was a swing problem initially, but it doesn't just happen with eighth notes, but I'm not sure how to lable the loping, uneven feel the incorrect playback produces.
Additionally, I tried creating new tracks and found that a new track with 170bpm with be played back incorrectly.  I did not have time yet to try every blm and determine where the exact line is. 
TLDR: I have refined my understanding of my problem to - tracks play back with uneven feel above certain tempos.
Any idea what could be causing this?  Is it a memory or buffering problem maybe?  I'm still stumped.

Have no idea. The new smaller default playback buffer has caused other issues which were resolved by setting it back to the old default (or higher). The setting is in Preferences > MIDI > Playback and Recording called "Prepare using nnn Millisecond Buffers". The X series default is 250. Prior to the X series the default was 500.

scook
...The X series default is 250. Prior to the X series the default was 500.

The 250 default only applies to the 64-bit edition. It's still 500 in 32-bit.

I tried increasing the buffer to 500ms but it had no effect.
I also noticed that on t least one file it does fine when only one track is playing, but as more tracks are added the playback becomes increasingly uneven.

Might want to provide more information about the system and the projects than just the behavior.

The files I'm working with are simple piano MIDI tracks.  But the files are irrelevant, I get the problem on new tracks as well.  Here is exactly what I am doing.
- Fresh install of CW (I uninstalled and reinstalled in hopes that it might resolve the issue).  Currently using the 64-bit trial version of the product.
- New project, Normal template
- Set tempo to 170bpm
- Display the default MIDI track in staff view
- Draw a series of eighth notes in the track (for the purpose of this test I drew six eighth notes in a row.  Pitch seems to be irrelevant)
- Add a Soft-synth track, set the instrument to piano:acoustic piano:mini piano(dry) - though I can reproduce the problem with other instruments as well
- Press space-bar to playback the MIDI track
- RESULT: the six eighth notes I drew in will be played back with uneven durations
 
With this method I can reproduce my problem 100% of the time on my system.  Any clues here?  As always thanks so much to anyone who has contributed their ideas to helping me.  It is greatly appreciated.

A few possibilities spring to mind....
 
MIDI buffers still set too low. Try 1,000.
 
PCI bus interrupt requests interfering with Sonar/Windows ability to stream audio in real time. Things  like wireless network adaptors are often the offender if that's a problem. There are downloadable free tools that can check for this, such as LatencyMon. There's also this one which for a long time was the most recommended tool and gives far easier to interpret results, but according to the developer it isn't suitable for use with Windows 8.
 
Could a dodgy MIDI clock source perhaps cause the symptoms defined?
 
Out of interest, does the metronome (settings are in the per-project part of preferences) play in time using both audio and MIDI outputs?
 
What happens if you bounce the MIDI track to convert it to audio? Do the audio transients line up with the grid correctly or are they displaced? If so, by what kind of amount? Same question if you "freeze" the synth.
 
Finally, details of the PC, Windows version, whether 32 or 64 bit Windows/Sonar and audio/MIDI interface might well be helpful to people trying to assist you.
 
And apologies in advance if you reply to me and I don't get back to you quickly. Going away for the weekend tomorrow and I don't know how good (or, most likely, poor to non-existant) the G3 mobile internet coverage is going to be.

Yes you have not mentioned your system, Do you have an audio interface? 
 
This is sounding like it has nothing to do with the age of the files. This sounds like you have not got a smooth running system.
 To bad you didn't save them as Midi files that would have been better for archiving.