Is your Indesign updated to 7.5.2 ?
Where are these file saved on network or on your computer?
Are you using any font mangement software link suitcase fusion.?
Saved on network
Enfocus Suitcase Fusion 3
System 10.6.8 - Snow Leopard
Converted problem files to IDML an reopened as new .indd files. Seemed to work fine.
Update to 7.5.2, and check with Extensis to be sure you have the most current patch for suitcase.
Also copy the file on the desktop and then check , issues are alos found when we work on teh file dirctly from network.