What do you exactly mean by the task is not being created? Do you get any
error messages when the schedule is being set for the backup to Disk? Does
the backup schedule operation seem to go through fine?
As another option to your need, you can use the database maintenance plan
wizard and try to create a maintenance plan to backup the database. This
will also create a sheduled task.
If the task is not created again, run dbcc checkdb (msdb) from isql_w
In the out put that you get search for any erro rmessages..(search for
"msg" using a notepad)
If you have any error messages, you might be having corruption in MSDB (the
db where all the scheduled tasks information is stored)
Let us know