Syntax error when trying to import database from two PostgreSQL databases
You seem to have omitted the new version of the upgraded server, but I strongly suspect it's still on 8.1 since the ALTER SEQUENCE ... OWNED BY clause was added in 8.2 (Compare ALTER SEQUENCE docs on 8.2 to ALTER SEQUENCE docs on 8.1).

You really need to understand that 8.4 and 8.1 aren't slightly different versions, they're massively different. It's like saying that Windows Vista and Windows 7 are "slightly different" versions because they're Windows versions 6.0 and 6.1 respectively. Or that Mac OS X 10.4 and 10.7 are "slightly different"... when they're more incompatible than not.

Yes, I know the version numbering in PostgreSQL is stupid; it's a historical oddity we seem to be stuck with despite periodic attempts to change it. See the version policy document linked in the prior answer for more information about what the versioning means, and read the release notes for a better understanding.