tomcat with firewall problem

[jacky ding]

Hi,dear all,I meet a problem about tomcat and firewall:
my company used apache+tomcat+jk2 to webserver,it inside the DMZ,and the Sybase database outside the DMZ.the webserver used JDBC connection pool of tomcat to connect database.
The problem is:when I start the tomcat service,and wait about one hours,the tomcat can not execute jsp that include database connection,but it can execute html and static jsp file(not include database operate).But when I had moved the webserver to LAN,it run ok,not any error!whether run time how long,it work normally!
So I check the firewall configure, and setup the access rule of webserver to database,adjust the option--max idle time,change it to 24 hour.But the error is still occur!!
If you have same experience,please help me!
Thanks you very much!