Hello Renee,

It looks like the task history database is missing or corrupt, you can do this to get a fresh database.
Make sure the task is stopped
Select the menu "Tools -> Explore Task Directory", this opens Windows Explorer, typically inside C:\ProgramData\WatchDirectory
Navigate to the subdirectory with the same name as your task
delete all files that have names starting with "history" (at least one, could be more than 1)
unzip this empty history.db: https://www.watchdirectory.net/img/forum/history.zip

Corrupt history can be caused by a server crash.

Not sure....
Maybe your disk is having issues? Run a checkdisk to see if that helps.
Or, perhaps, another program conflicts? Make sure to exclude WD's Task Directory is excluded from, for example, virus scans.

If the above doesn;t help you may have to reinstall on another computer - http://blog-en.gdpsoftware.com/2008/08/move-your-watchdirectory-install-to.html