Hi pariah and welcome to the community!
The message is just a general warning message, as there is no 100% compatibility when exporting to .ppt files.
However, from my experience, compatibility is very good and works in most cases, even for complex presentations.
Which exact version of OpenOffice are you using? You can check it via Help > About
You may try to upgrade to the newest version 3.0 or to 2.4.2 if you like to stick to the old line (which may be advantageous as version 3.0 has some considerable bugs).
Both versions are available from the official download site
Have you inserted the images as links? Maybe this causes the problem (although linked images are normally embedded when exporting to .ppt files).
You can check this via Edit > Links
. In case there are any (if there are none, the menu tiem Links
is greyed out), then you can try to break the links before exporting.
If this doesn't help, I suggest that you post a sample .odp document here, if you agree to disclose it.
This is done by clicking on the Upload attachment
tab below the editing window when writing a post.
If the file size is larger than 128k, use some file sharing web site like mediafire.com