Hi owlingz, and welcome!
Quoting from this KB Article about error 8506,421:
"There is a known issue with Norton security software and the Instant Reset utility distributed on some Lenovo laptops. Symantec is working on reproducing this issue. Unfortunately, in the meantime, Symantec recommends not to install Norton products on Lenovo laptops with Instant Reset functionality"
If the above reflects your situation, you could try following what suggested in said KB and see if it fixes your issue.
Before starting, please pay attention to the note at the beginning of STEP1.
Let us know how things go.