Attachment not saving to Step

This is the kind of problem I hate because i can't find anything solid to correct.  What we have is the failure for certain documents (PDF or DOC) to save to a Step.  We have been able to get other documents to attach BUT not the right one.   It is not the size, or characters in the name.  I've saved the PDF to an earlier version of WORD but still nothing seems to work.

We have been able to attach documents to other Plan Steps in other records.  

Any ideas?