The recommended way to create an Application Event Log using wix seems to be
<Util:EventSource
Name="BLAH"
Log="Application"
EventMessageFile="[NETFRAMEWORK40FULLINSTALLROOTDIR]EventLogMessages.dll"/>
On 64bit OS you replace it NETFRAMEWORK40FULLINSTALLROOTDIR with NETFRAMEWORK40FULLINSTALLROOTDIR64.
I have noticed that when you run a 32bit app on a 64bit OS it creates an event log with NETFRAMEWORK40FULLINSTALLROOTDIR when your use the .NET EventLog.CreateEventSource method from code.
EventMessageFile => C:\Windows\Microsoft.NET\Framework\v4.0.30319\EventLogMessages.dll
If you run a 64bit version of the app with no eventlog it will create it so
EventMessageFile => C:\Windows\Microsoft.NET\Framework64\v4.0.30319\EventLogMessages.dll
Regardless of whether the EventMessageFile has Framework or Framework64 in the path both 32bit and 64bit versions of the app can write to it merrily once it is created.
Is this supported behavior? What is the correct way to create it if one were to allow both 32bit and 64bit versions of the app side by side ?