I have had this today only for traps, not a fix but a work around if you need to do it immediately, Here's what I did, rather than using the Database Management tool I logged onto the database server and used SQL Server Management Studio:
First verify how many records you are going to delete (obviously substitute dbo.Traps for dbo.SysLog):
select count (*) from dbo.Traps where datetime <= dateadd(dd, datediff(dd,0, getDate()-7), 0);
Once you are happy with the result replace select count (*) with delete, this will keep the last weeks records and delete everything beforehand.
As the article says you need to then clean up the TrapVarBinds table (not relevant for yourself but I'll post anyway):
select count (*) from dbo.TrapVarBinds where TraID not in (select TrapID from Traps)
will give the number of records to delete, again replace select count (*) with delete.
No worries, happy to help!