Thank you for your replies. Really hoping it is the throttle, cap, or Hits not being available reasoning behind the message.
When you get that message, there should be a "Why" link in parenthesis after it. It explicitly states the meaning of it.
If you click on it, this is the information given:
"Why did I receive a message that "There are no HITs in this group available to you at the moment"?
Worker customers can receive this message for a number of possible reasons. This includes:
- There are no more HITs available to Workers for this HIT group.
- You have accepted each HIT in the group. Each HIT has been submitted, returned, or has expired.
- All the HITs in the HIT group have been accepted by Workers.
- The HIT group is experiencing extremely high demand and is not available to new Workers at the moment."
So, in other words, you've nothing to worry about.