Error running the Package: The variable cannot be found

I'm trying to run a package by asp.net web App and  I'm getting an error. The interesting thing is, It runs very fine on my Dev db instance but errors out on prod db instance. I checked all the settings of the accounts/package properties are the same.

Here is the code I've used:
 Dim pkgLocation As String
        Dim pkg As New Package
        Dim app As New Application
        Dim pkgResults As DTSExecResult
        pkgLocation = _
              Server.MapPath(AppSettings("PackageLocation"))
        pkg = app.LoadPackage(pkgLocation, Nothing)
        pkgResults = pkg.Execute()
        If (pkgResults = Microsoft.SqlServer.Dts.Runtime.DTSExecResult.Failure) Then
            pkg.Variables("ErrorDescription").Value.ToString()
        End If


And here is the error message I'm getting :  (By the way there are no variables used by the package)
"Couldn't Run the Package: The variable cannot be found. This occurs when an attempt is made to retrieve a variable from the Variables collection on a container during execution of the package, and the variable is not there. The variable name may have changed or the variable is not being created."