A deferred execution custom action that either accesses or sets a property is not working.

This is happening because custom actions have limited access to properties during the script execution phase of the installation. The script execution phase is when deferred custom actions are executed. The properties that are accessible to the deferred custom actions are ProductCode, UserSID, and CustomActionData. Deferred custom actions cannot set any properties.

Setting properties

Your deferred custom action can get properties other than ProductCode and UserSID by using the CustomActionData property. If you set a property that has the same name as your deferred custom action before script execution starts, the value of that property will be available to your deferred custom action in the CustomActionData property. You can do this by creating a custom action that sets a property, such as this one:

You can create this using the custom action wizard. Select "Set a property" for type and make [INSTALLDIR] the target. Accept the default choices for the rest of the options. Insert this custom action into the Execute sequence after LaunchConditions. When you run the installation, this immediate execution custom action will set the property DeferredCustomActionName to the value of INSTALLDIR. When script execution begins, the value of DeferredCustomActionName will be available to the custom action named DeferredCustomActionName in the property CustomActionData.

Getting multiple properties

If your deferred custom action needs to access to more than one property, you will need to pack all of these properties into CustomActionData and then make your deferred custom action "unpack" them after it gets CustomActionData. Here is a version of the property setting custom action above, modified to handle multiple properties.

Dim PropArray
PropArray = Split(Session.Property("CustomActionData"), ";") 
INSTALLDIR = PropArray(0)
SetupType = PropArray(1)
OTHERPROP = PropArray(2)
'Now do stuff with these variables...