Only PDF and PPT have problem, the rest can be opened normally. For PDF and PPT, when I open it, there is a question mark shown on top then the content are shown as plain text with error prompt up "An unknown error has encounter". For other users, same error and question mark prompts then cannot open these two attached file types. I found there was someone else had this problem before, I followed his solution as below but still not work.
When highlight the attachment file in BB handset, it always shows an icon on the top right hand corner. For PDF, it shows same icon as word doc then it displays in plain text format. Seems like it recognizes itself as a wrong format as word not pdf. For PPT, it has an icon with an orange color slash.