Symptom
DPR-ERR-2072 error The request failed. It was directed to a server that is not reachable.
OR
RSV-SRV-0040 An application error has occurred. Contact your Administrator.
 
Problem
After adding additional dispatchers all reports fail:DPR-ERR-2072 or RSV-SRV-0040
When only one of the dispatchers is running the error does not occur. When a second dispatcher is enabled all reports fail. 
 
Cause
The CAF (Cognos Application Firewall) was disabled on the original dispatcher. The newly added dispatchers were configured with enabled CAF. The CAF should set consistently in cognos configuration for all components in a distributed environment. 
 
Solution
Enable or disable the CAF on all servers
Steps:
1. Open cognos configuration.
2. Expand the tree to...
3. Security > Cryptography > Cognos Application Firewall
4. Set 'Enable CAF validation' to True.
5. Save configuration
6. Restart Cognos services