I create a table with:
CREATE TABLE "tab" ("asdf" SERIAL, "asdf2" char (20) NOT NULL );
Then I try to insert some data:
INSERT INTO "tab" ("asdf", "asdf2") VALUES
(NEXTVAL('""tab_asdf_seq""'::text), 'asdf')
ERROR: Relation '"tab_asdf_seq"' does not exist
(done with phpPgAdmin 2.3)