This error can occur if there is a speck of something on the aluminum or white backing strip. Open the cover and make sure that white strip and aluminum on either side is very clean. The optics scan this strip and builds a "profile" of what this looks like. It uses this profile to detect the paper once it is inserted. Dust or debris can cause this type of error to occur. You will find instructions for opening the iSis in the quick start guide.

If this is a Rev.E iSis or iSisXL (serial number above 3300), the software being used (i1Diagnostics, ProfileMaker5, ColorPort, etc...) might not have the proper DLL file (PC) or framework (Mac).  Please see the Related Support document at the bottom of this page entitled: "Connecting a Rev.E iSis or iSisXL to a Comptuer".