Statement 1: Two major dimensions of advertising are message creation and message dissemination.

This statement is correct. In advertising, the two major dimensions are the creation of the message (i.e., what the advertisement will say) and the dissemination of the message (i.e., how the advertisement will reach its target audience). These two aspects of advertising are interdependent and both play critical roles in the success of an advertising campaign.

Statement 2: Message creation is meaningful once the advertisement is created.

This statement is incorrect. Message creation is a critical part of the advertising process and its importance extends beyond the creation of the advertisement itself. The message should be carefully crafted to communicate the desired message to the target audience and to achieve the desired response. The message should also be tested and evaluated to ensure its effectiveness and to make any necessary changes or revisions.

Hence Statement 1 is correct.