When using a Ribbon Button in the Unified Interface an additional step is required - this is to set an Enable Rule for SelectionCount. Without this being set, when you select a record in a grid, the Ribbon Button will be hidden.
The North52 BPA solution works like this:
- Open your Command in Ribbon Workbench and click on Add Enable Rule
- Set a name for the enable rule (in this example I am using new.account.N52.SelectionCount)
- Make sure Un-customized is set to False and click on Add Step
- Choose SelectionCountRule from the options that appear in the popup menu
- Set the Default to True and AppliesTo to SelectedEntity
- Publish and the rule has been added to your command!