expression has an invalid type or reference ??????

[Odedra, Menand]

Hello All
 
I was hoping for some help with the above error message.
 
I`m attempting to pass a container element as an expression to a task, in
order to determine the agent.
The container element has our user id as the value.
 
i.e. &Requestor1& = UKMODE1.
 
If I hard code UKMODE1 as the agent
e.g. user - UKMODE1,
the task works fine.
 
Am I doing it wrong?
Should I be using Roles instead?
 
Thanks
 
Regards
 
Menand Odedra
Kraft Foods UK
Analyst Programmer (Supply Chain)
email: modedra at krafteurope.com
Tel: 01242 28 4748