Hey LoZ,
I work for a large wireless provider and often times have to figure out ways to make apps work properly with user interfaces that manufactures produce for operating systems. My personal phone is produced by HTC as well, and after the last update, I noticed the app was force closing a remarkable amount. The solution that I came up with was to go to settings> applications> manage applications> user installed applications> select Geocaching> Clear data. This will remove all user information, so you will have to re-sign in. Since doing so I have yet to have it force close. I came to this solution even after uninstalling the app and re-installing it. Hope this works for you as well.
ExhaustScum