In all the years I've used Sonar, I've never figured out hot to do this: have two projects open at once. I need to correct a bunch of stuff I mistakenly quantized. Can't figure out any other way but to copy and paste the notes from another copy of the project. I can't undo the quantize because I already closed and reopened the project.

U could just export it as a midi file.. If thats what u mean anyways.. then re import it to the track you want in the other project. As for opening a 2nd project I usually do it by just... opening another project. It opens right on top of the old one.

Thanks for that suggestion, Woody. The problem is, this isn't just a track or two. It's an orchestra. not every measure is messed up, but enough are that I need a quick way to replace the bad ones.
When I open another project, BTW, the first one always closes. Not sure what I'm doing wrong.

OK, I got it. I opened both projects, and can now "toggle" between them. So I can copy from one and paste to the other. They open instantly (actually I guess they just get pulled up). Problem solved. But some advice: careful with quantizing! Make sure the results are good. before closing the project!

You can also tile the windows and drag between them. But I usually use the Copy-Ctrl+Tab-Paste method so I can set the Now time precisely, given that un-quantized MIDI doesn't usually start right on the beat.
 
Another option that could save time is to drop the whole source project into the target project, and then shift+drag clips from source to target tracks. I haven't ever had to move enough tracks to make this worthwhile, but it might be the way to go in a big project.

Thanks brundlefly. I've worked my way through the woodwinds, and also have the violins done. I'll catch up the rest tomorrow. Just goes to show, you can sail along for years without a major glitch, and something can rear up and bite you. I will probably lose 4-5 hours to my stupidity. Oh well, can't complain, I'm retired. Have nothing but time (but somehow you still never have enough...).