Sounds like it could be an issue with the file. I'd try opening the file in CS5 first, then export as IDML.
Open that in CS5.5 and relink all the images. And then save it. See if it makes a difference.
If it doesn't then try exporting the file from CS5.5 to IDML and then open that and see if it fixes it?
What OS are you using? I've heard this issue before but only with Mac users on Lion. I'm sure I've heard this issue too with Mac users who use a Windows server…