I have tested what you report but I'm not able to reproduce. Photoshop Elements 8 was able to write the Keyword tags to files with both the JPG and jpg file extensions. I simply took a file with a jpg, copied it, and renamed the second copy so that it had the JPG extension. Then I imported these into Organizer, added a couple keyword tags, wrote the tags to the files and check the keywords in Bridge. Everything was fine. Perhaps there is something more going on here. Why do some of these files have an all capital extension? Where did these files come from? My guess as that these are from a scanner and what may be happening is that we are having a conflict with existing metadata on these files (scanners often add extra metadata and sometimes this has been known to interfere).
Could you post one of the files that you cannot add the keywords so we can test on our side?
Brett N, Thanks for help. You are right about scanner. In fact I found that all the JPG files were Read Only files. Obviously this was why the tags weren't being written. Why they were Read Only I've no idea, except they had been from a scanner! I should have thought about that earlier. Thanks again. Peter