Troubleshooting this is depends on if this guy is a push or policy (or policy supported push). In the event that this is a policy, there are some cases where the policy gets put down on the client by running policy.sync. Once policy.sync picks it up it gets put in the database. There have been some instances where even though a task is deleted from the console it doesn't get deleted from the client's database. So, if this is the case you can either look at the client database and delete the rows that refer to the task in the client database (see http://community.landesk.com/support/docs/DOC-5940 for more information on that) or you can simply run a script that does this for you (see below).
Here is a popular script that does the trick nicely:
cmd /c del "c:\documents and settings\all users\application data\landesk\managementsuite\database" /q
del "C:\Documents and Settings\All Users\Application Data\LANDesk\ManagementSuite\landesk\files" /q
del "C:\Documents and Settings\All Users\Application Data\vulScan\*.xml" /q
del "C:\Program Files\LANDesk\LDClient\sdmcache\landesk\files\*.xml" /q
net stop "Landesk Policy Invoker"
"c:\program files\landesk\ldclient\clientdbutil.exe" /create
"c:\program files\landesk\ldclient\clientdbutil.exe" /validate
net start "Landesk Policy Invoker"
EXIT /B 0
However, before for you go through that trouble verify that the task is indeed out of the database (the core's database that is). You can do this by going into SQL and opening up query analyzer and running the below SQL statement:
SELECT * FROM LD_Task WHERE Task_Idn = 235
The Task_Idn will vary from task to task, so in other tasks you can just look at the task ID and that will equal your task_idn. One thing to note is that you can't just go delete this row from the ld_task table, as there are several dependent tables. If this does indeed turn out to be a case of an orphaned task I will post a script to remove the task.
Let us know how you make out.