Please try the following in this order
1. Restart the App
The best option if the iPhone app keeps crashing is to switch the application off properly and then open it again.
Pre iOS 7- Double Click home key until you see a red minus sign on the application and click that. Hit home key again
Post IOS 7 - Double click home key until you see the apps tiled on screen. Drag the application to the top of the screen until it disappears. Hit the home key again.
2. Reinstall the App
If the above doesn't work -
a. Delete the application
b. Switch the phone off and then back on again.
c. You will then need to reinstall the vWork application from the App Store.