Try exporting it to idml or inx from CS4 and opening that in CS5.
Some screen shots would be helpful, too.
There is a known issue with tabs in certain circumstances (that often show up in menus). I don't recall the exact details, but I think they involve two tabs on a line and using leaders. I'm also not certain this shows up until the file is exported to PDF.
Are you patched to 7.0.4?