VideoStudio :: X3 VSP Files Won't Open In X2?

I have both VS X2 and VS X3. I've been working on a project in VS X2 for the last month. I just recently installed VS X3. I opened up the file in VS X3 for the first time, saved the project. Now the file won't open up in VS X2. I tried with another short project file that i originated in VS X2, opened it up in VS X3, did nothing to the file, saved it in VS X3, and now this file wont open in VS X2 anymore either. It seems that when I save a file in VS X3, whether i edit the file or not, the file will no longer open in VS X2. All files are the standard .vsp files.