Ajay, I finally figured out why I was having problems with the upgrade. I think this will be useful info for you. I decided to upgrade VegasNews.com to WP 3.4 before trying another upgrade to CRP 1.83 (from 1.8 which was still working). When I tried upgrading, once again the thumbnails were gone. It turned our there were two minor issues that together really fooled me.
1. During the upgrade, the Timthumb directory gets rewritten and the default permissions prevent Timthumb and its cache from working. Changing to 777 allowed thumbnails to be made again. But some were still missing here and there.
2. And here's why. You do a great job of saving the CRP settings during the upgrade, including the fact that you retain the link to a custom "no image" png. But during the upgrade, the CRP directory is overwritten so the custom png file is deleted. With the custom CSS settings that I have you can't really tell when a thumbnail is missing or if the custom png is missing. As soon as I replaced the custom png, everything displayed properly again. I guess I could put the custom png somewhere else but I just now thought of that. :(
The bottom line is that it's not a CRP problem but if your upgrade routine could deal with these issues it might reduce some confusion.
Once again, CRP is one of the best plugins of all time! Thanks again for all your help.