I think that you will find that Gigabyte's equivalent aged mobos (I think that abit stopped making AB9s over 18 months ago) don't support E7400s either.
Given that all the info about CPU support is on abit's website & it's been widely known for months that abit were out of the mobo business by the end of 2008 if you've just bought this board then
imo I'm sorry but it's your own fault.
If you speak nicely to your supplier maybe they will let you swap?
if it doesn't support EOs how likely is it to support the later ROs ...?