I always set autosave to seasonal to minimise lost time. May even want to change compressed saves to uncompressed incase something got corrupted while saving but I don't 'think' that's your problem, however it does seem to be a save issue
I did have something like this when transferring an edited and modded save to a new DF version, but then I changed graphic sets
and updated the mod. Had to edit several of the save file's raw/objects to change creatures back to mostly how they were to get it to work. I think this error references a mismatch in creatures? As in, the expected creature in the save .dat files is now different than or missing in the save/region#/raw/objects files? I recall that thread suggesting you were editing the elves to make them more likely to siege you? Unfortunately I think this has modified them too much from the
save itself. To fully implement them you'd need to change the worldgen raw/objects to those changes and gen a new world. You could fix the saves however and not crash at the siege by using
http://WinMerge.org to compare old and new files to see what's missing/changed and continue the war with the damn stinking elves ;p. Only certain tags would need to be added back in I think, so you could trial and error the differences. Used it to fix my "NEMESIS LOAD FAILURE" and several missing material/object errors that also crashed it.
One last thing I can think of which can give that error but I don't think is your issue anyway, thought I'd post it: it's possible the DF or LazyNewbPack download was corrupted and has a different checksum than the original. If it's vanilla you could try downloading it again. If it's LNP you can look at the dffd download page(for your version) and compare the SHA-256 hash of the archive(.zip) you downloaded with the listed one by using
http://OnlineMD5.com. You can just drag the file over, then copy and paste the hash from the dffd page to compare with. I doubt this is the case but I've had that happen twice and be the cause of crashes and odd errors in about 3 years