"This issue can't be scheduled because no one is available"- upgrade capacity is not useful?

[Giangi Pbrasili]

I receive on some Issue the following:

MessagesLevelDescription

This issue can't be scheduled because no one is available

ERROR

Check that someone in your team is available to work on this issue at this time and then recalculate your plan. Learn more about availability

I try to modify the capacity adding a "new team manager" but the system don't schedule the issue any way.

Have you any suggestion ?