Cannot register SPN, error 0x80090350, state 4
The error message you're seeing, 0x80090350, is defined as:

c:\util\Err&gt;err 0x80090350

# for hex 0x80090350 / decimal -2146892976 :
  SEC_E_DOWNGRADE_DETECTED                                        winerror.h
# The system detected a possible attempt to compromise
# security.  Please ensure that you can contact the server
# that authenticated you.
# 1 matches found for "0x80090350"


I'm looking this up with the Exchange Error Lookup Tool.

According to the information in this post, this error is often caused by the MaxTokenSize issue caused by an account (indirectly or directly) being a member of a large number of groups. 

Another possibility I'd consider is that a duplicate SPN exists. You can determine which SPNs Windows thinks are duplicates by running setspn -X -F (info here).