The only thing that I find which works for me is to 1st make sure that your Kustom folder is backed up to your Computer, External storage or wherever then delete as many of your old, unused themes as possible. I have a tendency to Edit one of my themes then export it with a new date. I end up with a lot of excess and will see the error message you displayed. Never hurts to go into Settings/Apps/KLWP/Storage then clear the cache. I usually don't have to clear data but if you do, it won't wipe out your folders with your themes.
Yes the latest release seems to have broken something so sometimes we can't pass a variable from Tasker to KLWP. It works sometimes with some variables but other times with other variables it just errors out (which causes the task to abort).
Don't know if this helps but this is the error message I get in Tasker: