I have the same issues, but for me it seems to happen after I preview the menu or do a build. In any event, I believe a video file is created for the menu and stored in the Sources\Video folder of your project folder. I believe the name of the file is determined by your video settings. My file is called mp24x3NTSC720x480.mpg.
The strange thing here is once it is created it cannot be deleted. Even after Encore is closed. There is a stuck process that is keeping it tied up and therefore, when Encore tries to recreate it in a new build or preview, it generates a general error. I am unable to identify the process in Task Manager, so I doubt that it is listed there. Could be a memory leak/error within the program. Something is not being closed in memory.
After rebooting the computer, the file is freed and able to be deleted. Encore then responds normally until it has to recreate that file which is again stuck summoning the general error.
No solution here, just an observation. Check it out on your system and see if you are getting similar results. Maybe Adobe can issue a fix to this seemingly notorious bug in their code.