Seems your /opt partition has problems.
If you reflash /opt you are also deleting the majority of those files in rootfs which are symlinked to /opt. So you better reflash both rootfs and opt and start over. Also, if you have a recent backup - or your n900 is still able to backup - at the time you restore, after reflashing, you get a chance to reinstall all the applications you had, or the select only some.