When your Iteration Status Page won't load, filter buttons don't work or the Work Item Type drop-down doesn't work, it is usually due to a corrupt filter setting which prevents the board from loading. Filters are saved as a Preference on a per-user basis. To clear the potentially corrupt filter setting, you can delete the filter preference. Each user experiencing this issue will need to walk through the process to clear their own preference.
See this video for a walkthrough on adding a custom app