system
4
I didn’t have anything else better to do, so I tried it on your behalf… 
I deleted a coupla startup items with the Ccleaner startup tool (see attached graphic), no problems. It might help if you can post a similar graphic, as well as a graphic of your error message.
Note that I run a barebones avast (see my signature below).
You might try disabling various avast shields/options. I would probably start by disabling avast completely, temporarily for 10 minutes, then see if you can use the Ccleaner startup tool. If NO, then it’s something systemic. If YES, then add back the various avast shields/options until you isolate the culprit. Just a hunch, be sure to test the scripts shield (part of the new web shield)…