Go to the general part of Jiminy's Journal. From there go to the "Nobodies" section in the journal and go to the very bottom. There will be an entry there that says "Twilight Thorn" which is the big white boss that Roxas had to defeat.

The error is that Jiminy was not with Roxas when he fought Twilight Thorn. In fact, Jiminy was never with Roxas at all, he first appears when Sora, Donald and Goofy awaken from the pods in the Mansion in Twilight Town.

Submitted by a_guy_named_me (tall_one37)