NAT working intermittently?

I have an application and the developer is trying to blame BIG IP for a connectivity issue. He claims that the problem started when I created the NAT for administrative access and so his application can talk to the SQL database. The thing is this NAT is working all the time for other applications on the same server and about 80% of the time for the application in question. Has anyone expireneced anything like this and any ideas on what to look at?