Here is an good example in the MLB rules that fits letsplat2's situation. This is also contained in 10.18 of the MLB rules.
quote:
EXAMPLES: (1) With two out, P1 walks A. B reaches base on an error. P2 relieves P1. C hits home run, scoring three runs. Charge two unearned runs to P1, one earned run to P2
In this case the error allowing "B" to reach base with two outs prolongs the inning and most assume that all runs scored after the error would be unearned. (they are from a team's perspective) But since P2 (the relief pitcher) cannot benefit from a previous situation in which he had no part, he will be charged with an earned run as common sense dictates he should.