You are unable to use the Task ID smartfield from the Workflow context browser when dragging the field in any mail task configuration.
- Ensure you have K2 Five RTM installed.
- Get the K2 Five RTM FP14 from Regional Support.
- Install the K2 Five RTM FP14 to apply the fix.
- Edit the workflow and remove the existing mapping of the Task ID field. Re-configure the mapping using the Task ID field again.