Agent not found - ErrorCode [0x03]

Symptoms

Target verification of published application fails with error "Agent not found - ErrorCode [0x03]":

RDSH Agent state in RAS Console is "Verified":

When you try to check agent status from context menu, status "Agent did not reply, please install Agent." is reported:

Cause

RAS Console fails to connect to the RDS host on TCP/UDP port 30004.

Resolution

Configure firewall to allow inbound TCP/UDP connections on port 30004.
Other firewall requirements can be found in this KB article.