I have documents from a client that were created in an earlier version of Indesign (I'm not sure if it was CS3 or CS4). I use Indesign CS5.5. I can open the documents OK and work in them without problem. (I have all the fonts being used, but some of the image links are missing) I'm adding pages and formatting text as I go. Then around 30 pages into the job, I find that I'm unable to undo or save any changes to the document. I've tried exporting to an IDML file and reopened it as an Indesing document and I still can't save changes.
Can anyone help me? Short of rebuilding the document from scratch, I don't know what to do.