The tomcat server when running this wrong, but returned to normal after restart the tomcat server, what reason is this excuse me?

[org. Logicalcobwebs. Proxool. ProxoolPool - sweep] - Prototype
Org. Postgresql. Util. PSQLException: The connection attempt failed.
The at org. Postgresql. Core. The v3. ConnectionFactoryImpl. OpenConnectionImpl (ConnectionFactoryImpl. Java: 292)

Database connection pool is as follows:
Proxool. House - keeping - sleep - time=60000
Proxool. Simultaneous - build - throttle=20
Proxool. Maximum - new - connections=20
Proxool. Prototype - count=5
Proxool. Maximum - connection - count=400
Proxool. Minimum connection - count=10
Proxool. House - keeping - test - SQL=select CURRENT_DATE from dual
Proxool. Maximum - active - time=30000
Proxool. The maximum connection - lifetime=1200000