Fix to GarageBand can not open files

Question

I followed many of the suggestion in the board and they did not work
-- delete files in ~/Libary/Preferences
-- delete reinstall GarageBand
-- play with permission
-- etc...
After all this, I found that the problem is when your login name (long name) does not match your home directory name (short name). They have to be the same.
Once I change the home director (as another sys admin) to match my login name, deleted by account and re-created same name account (will prompt that directory exists and do you want to use -- say yes) every thing worked.

Answer 1

After all this, ######I found that the problem is when your login name (long name) does not match your home directory name (short name). They have to be the same.
I am not convinced of this solution, sorry:
I don't doubt that this did fix the problem for you, but the login name (long name) does not have to be the same as the name  home directory name (short name). If that were the case, it would not make any sense to have a long name and a short name. My long name is different from my short name, but I can use all my GarageBand projects without problems.
When you changed the home directory you probably changed it to be exactly the same as the name of the owner of your GarageBand projects, and now you had the right to access these projects.
You need to be the owner of your projects or to have read and write permissions granted to you.
You can check the permissions in the Info panel (File > Get Info ⌘I) for your projects by disclosing the Sharing&Permissions brick (click the padlock to make changes and authorize as admin ). If you find, that you do not have read and write permissions, click the "+" and give yourself the permissions.
After adding permissions click the cogwheel and select "apply to enclosed items" and "make yourself ower", if the option is available.
Regards
Léonie