I’ve seen some crash reports on iOS5 with the following error:

‘NSInvalidArgumentException’, reason: ‘Cannot set metadata in read-only store.’

Looking at this thread and the dev forums, it seems like an Apple bug, but one user said:

My beta testers reported that syncing with iTunes seems to clear this error up- so my guess is that iTunes sync is fixing a permissions problem.

Let’s hope they’ll fix that in a next release, since it’s about 20% of the crashes for 2.9.1 right now