DTEXEC.EXE Argument for option "set" is not valid.

this is probably an easy one but i can't figure it out ....

simply executing an ssis package with an argument

DTEXEC.exe /FILE 'C:\test\CONTROLLER.dtsx' /SET '\Package.Variables[User::Email].Properties[Value]';'test'

DTEXEC.exe /FILE 'C:\test\CONTROLLER.dtsx' /SET "\Package.Variables[User::Email].Properties[Value]";'test'

or 

DTEXEC.exe /FILE 'C:\test\CONTROLLER.dtsx' /SET "\Package.Variables[User::Email].Value";"test"

or

DTEXEC.exe /FILE 'C:\test\CONTROLLER.dtsx' /SET "\Package.Variables[User::Email].Value";'test'

they all returned the following 

Argument ""\Package.Variables[User::Email].Value"" for option "set" is not valid.
test

this is the version of my dtexec 

Microsoft (R) SQL Server Execute Package Utility
Version 13.0.1601.5 for 32-bit
Copyright (C) 2016 Microsoft. All rights reserved.

any ideas what i might be doing wrong?

thanks

eddy

eddy.a