The dateline index does not exist in default vb, I think the mod included instructions to add it at one point but I'm not sure.
Anyway, just use this SQL command ;
[sql]ALTER TABLE post ADD INDEX (dateline) ;[/sql]
However, since you are both running vb 3.6, so you should really be running this version of the mod (which as I said, creates the index automatically).
https://vborg.vbsupport.ru/showthread.php?t=123886
The version you are currently using is
very old.