Bill:
Compare the size of the file in question to another project you have done with the same instruments/length. If it still seems too large, then it may be damaged in some way. Most of my songs are 3 to 4 minutes with up to 12 audio tracks and none of them have a .WRK file larger than 5k. It wouldn't hurt to enlarge the buffers...if it doesn't help, you can always put the original values back.
The only other thing that I can suggest is to run a good virus scan/clean program on your files. Also, run a thorough scandisk (double click on "My Computer", right click on the hard drive icon, go to properties, click on the "Tools" tab, and click "Check Now".
If it still won't open, the long shot is to use Norton Disk Editor. I have had limited success fixing files with it...most of the time the file gets screwed up worst than it started, so always work on a copy of the file and not the original. To edit the file back to life almost requires that you have another file (in perfect shape) almost identicle to the problem file that you can look at and compare to.
Cakewalk has a tool called "Clean Audio Disk" (under "Tools"). It will find temporary .WAV files that it uses as undo files. If you have the patience, you can play each one of them...you may find some of the tracks to your project there, and rebuild from scratch.