email attachments

when i send email  with attachments to others some of the others are telling me that they cannot open attachments. .

I tried what aadeshs76610910 advised to run the repair the installation. I advised him that problem was solved. but it is not. several people that i emailed with attachments are telling me that they canno open attachments.

could this be because i am using windows and they are using mac . before i upgraded to reader dc i used reader 11 and had no problems or complaints. how can i correct?