I've just discovered a BIG massive bug whenever it comes to the RunOnce and msi files. Basically it will run an msi setup but not wait for it to finish before continuing onto the next installer. The msi installer currently running can prevent others from installing. Especially if all of them are msi files. This has been fixed and I'm currently testing UPDATE 1: It also affects CAB files. UPDATE 2: This has been fixed in the latest test build which can be downloaded here.