Why do apps from Android 2.1 stop working with 2.2?

I've just updated my nexus one to 2.2. Now all of my (own and some from the market) apps throw exceptions and were closed.

It's weird, in开发者_开发技巧 the app I'm developing atm, there it displays only my start page with buttons, but when I tap on one button to fire an intent to another activity my app gets closed with an exception.

Yesterday before the update everything worked fine.

The same thing in my emulator:

I have two devices, one with API level 7 and one with level 8. Level 7 worked fine, but level 8 killed my app :(

What is the problem and how can I solve this? I'm desperatly trying to get it working again :(

I hope someone can help me fixing this

So, like in my comment above I write it right here as answer:

The problem was that the SD was mounted as mass storage device on my pc, while I was trying to access it by my app -> Error, because SD was not accessable from app

In fact, it had nothing to do with the version (see comment from Roman Guy). The problem just occured the first time, two days after I updated the device ;-)

I hope someone can benefit from my stupidness ;-)