Change custom entity fields
I finally solved this problem somehow.. I think this is an EntityAPI's issue. So, here is my (temporary) solution:


removed those changed fields directly from hook_schema, added new fields directly to it.
removed those fields with db_drop_field function and added new fields with db_add_field function with hook_update_n function. By this way I managed to have the same structure in my (changed) entity and db table schema.
flushed the caches


Error has gone, so far everything is working fine. But I'm not sure this solution will not cause any problems in future... I still can't understand why entity api doesn't see changed fields in hook_update_n function...