The path would be in the error message also if you'd write a non-existent path in the format string. This could then also be freely posted and quoted by everyone. It simply doesn't help to help you.
My guess is that instead of
C:\Users\leeuniverse\Desktop\
it's actually
C:\Users\leeuniverse\Desktop\80s Music\
Wow... Ya, it was me... I figured it out just before you posted.
I don't know "how" it happened since I selected the folder in question, but ya, "Thumbs" wasn't in the file-path...
I'm truly sorry... I didn't sleep at all, and I just somehow missed it.
Really sorry for the stress I caused... Fixing the path corrected the problem.
In conclusion, adding %artist%.jpg to the end of the path for the Action in question was the solution to the issue.
Again, I apologize, massive mistake on my part.... Ugh...
No problem, happy it's working now 
BTW, for those who might want to know...
You can use %albumartist%.jpg instead of %artist%.jpg if you're like me which has the primary artist/group ONLY listed in the Album Artist Tag, so sometimes the Artist and Album Artist can have different info.