Situation: Lets say 2 outs, E-6, followed by a single, BB, HR (equals Grandslam). Are the runs that followed the error that should have ended the inning earned?

Not earned.
Saw that happen a few times. Any runs after the E that would have ended the inning are UE.

BobbleheadDoll is absolutely correct.

In an interesting twist, suppose pitchers are changed after the single, before the BB. Relief pitcher comes in with two on, walks the first batter and gives up the HR. In this case, the starter would get charged with two unearned runs, but the two runs (BB & HR) would be earned for relief pitcher per Rule 10.16(i).

Comment 1 has almost the exact situation as an example:

It is the intent of Rule 10.16(i) to charge a relief pitcher with earned runs for which such relief pitcher is solely responsible. In some instances, runs charged as earned against the relief pitcher can be charged as unearned against the team. For example:
(1) With two out and Peter pitching, Abel reaches first base on a base on balls. Baker reaches first base on an error. Roger relieves Peter. Charlie hits a home run, scoring three runs. The official scorer shall charge two unearned runs to Peter, one earned run to Roger and three unearned runs to the team (because the inning should have ended with the third out when Baker batted and an error was committed).