Overview
Sometimes an app will force close right after you update it from the market. In many cases this can be fixed.
Power Cycle Phone
Turn the phone off and then back on. Try the app again.
Clear the cache
Menu->Settings->Applications->Manage applications
scroll down the list of apps til you get to the one that is a problem and tap on it. You will now be viewing the details related to that app.
Try clearing the cache for the app and then see if ti will now run.
Uninstall/Reinstall
The last option is to uninstall the app and then reinstall it. This works in many cases, but can cause you to lose settings and data.