Let's pick an easy one and see if we can fix it - RegIdleBackup.
That is the task that every 10 days takes a snapshot of your registry files and save a copy in this folder:
c:\windows\system32\config\regback
Take a look out in that folder and see a copy of the 5 registry files.
Some folks say that backup occurs "sometimes", "every now and then" and "once in a while" but it really occurs ever 10 days according to the task parameters.
In your Task Scheduler, find that task, see if you can right click and Run it or not...
Then right click it and Export it someplace safe (just in case) and it will be saved as a .XML file:

The Delete the suspicious Task.
In an empty spot that same Window right click and choose to Import, change to 'All files...', and navigate to the folder where you unzipped the Windows 7 Tasks from The Repair Tasks download (mine is on my desktop) and choose the RegIdleBackup file, click
Open:

Before clicking OK, click on Settings and enable the Task to run on demand, then click OK to save it:

The right click the Task and Run it, click Refresh (or press F5 to refresh) and see how it looks:

Then if you look in c:\windows\system32\config\regback folder the files should have today's date and time. Yea!
If that task is working now, do whatever you have to do to see the 20 afflicted tasks and see if now there are only 19 afflicted tasks (may need to reboot).