I was running into a similar issue and really banging my head against the desk...literally.
I noticed at least one person with the same issue I had. Case sensitivity. \Package.Variables[variable_name].Value
I feel really dumb for wasting half an hour figuring this one out. I also feel better, however, knowing I'm not the only one. 😛
I really do wish there was some sort of consistency in the MS world regarding case-sensitivity.