I had this same exact problem for the last several days and just figured out how to fix it. It is a permissions problem. You can't change a task or create a new task in Task Scheduler because your user account on your PC doesn't have sufficient permissions to make use of the Tasks folder on your computer. Panda may be changing the permission on system folders so that they can't be accessed, but I'm not sure. I'm using Comodo Internet Security 6 and it loves to change permission on all sorts of folders on my system drive without asking me and locks me out of them. To be able to access a folder again, I have to change ownership, them change permissions on it.
If you don't know already, the folder that Task Scheduler is using is C:\Windows\System32\Tasks, at least it is in Windows 8. I'm assuming Vista is the same way. In Windows Explorer, right click on that folder and click on "Properties", then click on the "Security" tab. In "Group or user names", find your user account. Check the permissions down below. If you see no check marks under "Allow" for any of the items listed, then click the "Edit..." button and give yourself full control then click OK. Click OK again in the properties window and you should be fine. I think this process is the same in both Win 8 and Vista, but I'm not sure.
After I gave my user account full control on the Tasks folder, the error window that popped up, which was the same as yours, stopped appearing and Stardock Central started updating itself like normal.
If a warning window pops up when you right click on the Tasks folder saying that access is denied and that you don't have any access to that folder, then you have to change ownership of the folder and then change permissions. If you don't know how to do that, here is a website that will explain the process: http://www.askvg.com/guide-how-to-take-ownership-permission-of-a-file-or-folder-manually-in-windows/.
If you already know how to do this, then I apologize for describing stuff that you already know how to do.
I hope this helps.
Dave
