You mean 1" short in the length for a 4 foot run or 2" for an 8 foot run?
You have a scan calibration (which is across the printer left to right) and a feed calibration (what the rollers do to feed out the media).
They are saying check the feed calibration in the service menu.
I think in rip menu's there is always a window for the media you are using. I used to always have mine (older printer in flexi) on other, but I think that is what controlls the feed compensation for each media. So if you have banner material loaded and using cal viny in the setting you will get the wrong feed rate.
However, 1" is a lot to be short so check the feed calibration. Thicker media feeds shorter than thin.
If all else fails when using that media adjust the file size for the feed length from 100% to 102.08% but not for the scan width.