Hi,
If the file is named correctly and the key has a value I cannot think of a reason it would display as blank. If you have a key AllowEmailLabel with a blank value then it would be blank, but if it could not find the resource files it should actually render the key itself.
Remember that if you make changes to your .resx file you need to re-copy it to Web/App_GlobalResources either manually or by building the project if you are using post build event to deploy it.
Hope it helps,
Joe