Memory mapped files in IIS

hello all,
I have a problem that drives me crazy. I googled around but could not find any solution.
From a regular .NET application, I am creating a memory mapped file. I can access this memorymapped file from other .MET applications, even running with different account.
However, when I call it from an aspx page, running on IIS, it gives me a FilenotFoundException.
The code is dead simple :

The application that is creating it :
Dim m As MemoryMappedFile
Dim sec As New MemoryMappedFileSecurity
Dim id As New SecurityIdentifier(WellKnownSidType.WorldSid, Nothing)
Dim rule As New AccessRule(Of MemoryMappedFileRights)(id, MemoryMappedFileRights.FullControl, System.AccessControlType.Allow)
sec.AddAccessRule(rule)
m ...