I've fixed it. The printer settings layout was set to "2 pages per sheet". I'm not sure how it got set like that (as it's a new printer) and I can't believe I didn't notice.

<t>Hello,<br/>
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I'm using Adobe Illustrator for Windows and a Rocoh SG 3100DNw to print onto mug sized sublimation paper. The printout is 90 degrees and squashed to the paper width - please see attachment image.<br/>
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My Illustrator artboard is 241W x 102H. The print media in Illustrator ...