Can't open attachments on e-mails from known/trusted sources.?

Question

Yahoo is our provider. It's been happening about a month; no problems before. I've lowered security setting temporarily, but still couldn't open. No new programs have been added within the last 4 weeks.

Answer 1

Opening attachments from ANYONE is at best a roll of the dice, and can be a total train wreck if it's not what you expected.

Where possible have the sending party post the subject material to a website (many free ones are avialable) for you to then access it.

Setting your securities looser at the local machine may not resolve the issue.  It may be block at the server (Yahoo).  That may be resolved in the settings for the account in the Yahoo Mail properties.  Open the Yahoo mail account, and look around for that group or headding.