What kind of attachments are you trying to open?
DOC/PDF/XLS/TXT should work.
BES 3.6 does not support image attachments GIF/JPG/TIF/PNG. You need BWC 4.0 or BES 4.0 in order to use image attachments.
However, you said it worked for two days, and then stopped working two days later. This would be a BES Admin Corner question... Moving this thread