iOS app hangs if left idle.

Hi, I'm getting this problem in the crash logs. The app just hangs after a few mins of being idle aka no one interacting with the app.

OS Version:      iPhone OS 5.1 (9B176)

Report Version:  104

Exception Type:  00000020

Exception Codes: 0x8badf00d

Highlighted Thread:  0

Application Specific Information:

Main[1303] has active assertions beyond permitted time:

{(

    <SBProcessAssertion: 0x4aedd0> identifier: Suspending process: Main[1303] permittedBackgroundDuration: 10.000000 reason: suspend owner pid:15 preventSuspend  preventThrottleDownCPU  preventThrottleDownUI

)}