If your provider( Cable/Dish) provides SEC + and you are not able to access call ESPN customer care @ 1-888-549-3776......9AM-1AM 7 days a week and they help get you on line.As another poster posted,clear your Watch ESPN cookies and reload app may work .
I had a similar problem since I have Direct TV and have Verizon for internet and phone.I tried to sign on thru Verizon since I have internet with them and thought that would be the thing to do .I got the same error you are getting and rejected my every attempt.I contacted ESPN Customer care and they set me straight that Direct TV was my provider not Verizon.I still have occasional problem getting SEC+ since they still have my provider ( provider is displayed in upper right corner of ESPN screen) as Verizon and I have to change it to Direct TV by covering the Verizon provider with my mouse and a provider screen comes up then I click on Direct TV and voila I am in.
If your direct TV is displayed as your provider in upper right of screen ,then you need to contact Direct TV to correct sign in pass word or to get registered properly so that ESPN recognizes you as an authorized
customer.
Hope you are able to get the Rubix cube solved because there are a number of games that will be on SEC+ in future.