HI Ben J,
I am facing the same issue and followed the same steps what are mentioned in both the SAP Notes 1622837 and 1639578.
After restarting the SAP, I checked both R3trans -d and R3trans -x and both giving RC as 0000.
Then I shutdown SUM tool and start it with a fresh login of sidadm but getting same below error page each and every time.
When I checked DBCONNCHK.OUT in log it shows RC 0012 for R3trans
Could you please let me know what's wrong happening and how to resolve it.
Regards