"insert comment" grayed out in my keynote file

greetings,

have been using keynote a couple years. am using the current version...

i've run across something odd that i haven't figured out yet... i created a presentation in keynote and am still working on it... i tried to "insert comments" on a couple slides. however the menu option & the icon in the toolbar are both grayed out... quitting keynote and restarting doesn't change it...

i can open a new blank file in keynote and insert comment box there... i can copy and paste the comment box from the blank file into the file with the problem. but the option to insert a comment from the menu and toolbar are still grayed out in the file i'm working on.

i'm getting a little concerned that there may be something wrong with my file. i exported a .pdf & .ppt, just to be safe in case the file become corrupted... i also normal keep versions of the file along the way in case i want to return to a previous version or in case a file become corrupted...

i have 2 macs, 10.5.8 on a PowerMacG5 and 10.6.2 on a MBPro... same version of keynote on both computers... the problem is the same with this file on both computers.

i didn't find any posts similar to this here.
- any body run across this before?
- is there a way to rebuild a keynote file?
- any other suggestions?

thanks for any advice-
jeffery