I create Installer for my company, with using SQL 2005 Express and its files database. I used MS Build bootstrapper before to install MS SQL 2005 Express in my installer and it was installed before my product installed, and there is no problems...
But now I need to install Express during setup, because it must be installed NOT everytime (if user choose, in bootstrapper it is impossible).
I know that during execute sequence it is not possible: two installer are not lived simultaneously in memory and I move SQL 2005 Express installation to UISequence.

But everytime error occured during install (list from sql server install log):
MSI (s) (00:6C) [18:54:38:015]: Machine policy value 'DisableUserInstalls'
is 0 MSI (s) (00:6C) [18:54:38:015]: Note: 1: 1309 2: 5 3:
MSI (s) (00:6C) [18:54:38:015]: MainEngineThread is returning 110
The system cannot open the device or file specified.

So there is no error, "Another installer process in memory", but another
very strange error and I dont know what to do
I try quiet and usual SQL express install - but that doesnt matter.

It seems, that package sqlexpr32.exe after unpacking cant see its files... What must I do to install SQL 2005 Express during my UI of Installer?

Or may some other ways to install SQL 2005 Express, with some secret keys?