Are you patched to 5.0.4?
Export both files to inx, re-open, Save As. (I checked, ID will not load styles from an inx)
Load just one style at a time to isolate a conflict.
Last resort, Highlight text from the source doc, paste into the new doc. I should carry in the style. It only needs to be a single charatcher.
Thank you , one of the paragraph styles was causing the issue.