I bought logic express a year ago and just noticed I was using 9.0 and tried to update at apple web site. I entered the correct Serial number that came with my CD, but kept getting a, invalid serial number message. I don't know what else to do know.
Software update will work as long as the Logic app is in the applications folder (and not been placed in a sub folder, like many people do). If you have done this, just move it into the apps folder, and hit software update. It should work.
I just made sure the only version of Logic I have is in applications folder and says 9.0. I then clicked update and it said there is nothing to update. I wonder if I am going to have to erase it all and re-down load the whole program. Also, I would be nervous to do this because at the Apple Logic Express site it says it does not know the serial number I type in to get the latest download.
I am able to now download updates, but my computer says Logic Express is not in HD applications. However I can open my Logic by clicking on Macintosh HD then click on applications, then click on Logic Express 9.0.0 It seems to me the computer doesn't acknowledge that the Logic program is in the correct spot for updates. I also read all of the past similar problems.