Here's a tip. If you are running an SD cloned multi-boot system, you have to maintain your partitions regularly. If your primary modest install is on a cloned SD partition and you are getting errors, try booting to flash and running fsck.ext2 on your partition. I had tons of errors, many of them in Modest-related files. It was so bad that after the fsck, I needed to wipe Modest off my system and re-install it. I think Modest does a lot of file activity, causing the files to corrupt.

Assuming your cloned OS partition is #2 on your card: