Update 5/3/2011: The fix (version 2.1) has been published to the market place. You should be able to start downloading it whenever your country's marketplace refreshes.
Well, it had to happen, eventually. There is a major bug in Version 2.0 of Stripes that is affecting users that upgrade from a previous version. Because some internal data structures have changed, when the old application state is pulled into the new application, items are missing and the application can crash when searching for a barcode.
A fix for this problem has been submitted to the Marketplace, but it may take a few days to actually hit the device in your hand.
A short-term fix for this issue can be performed by uninstalling Stripes and re-installing it from the Marketplace. You will not be charged for the re-installation and it should fix the internal data structure. However, this will result in complete data loss of your scanning history.
I apologize for this error and please look for the fix on your device, soon.