There is an unfortunate bug in the most recent 1.6.2 update. To fix this, please do the following:
1) Open the Settings.app from your iPhone
2) Scroll all the way down to Week Cal
3) Go to Behaviour
4) Set Badge to "none"
5) Week Calendar should work now
We've already sent a fixed version to Apple and are at their mercy to get the fixed approved as soon as possible.
Our deepest apologies for this problem.