Trouble opening jpg files or pdf files in Outlook 2007

I have a new machine running Windows 7 and Outlook 2007. If a picture is inserted in a message it comes through fine, but sent as an attachment most of it is "greyed out". The picture itself is not corrupt because I can view the attachement in the same messgae looking at it on my IPhone.

The same is happening with adobe files attached sent to me as an email attachment.

I am using MS Firewall and MS Security Essentials for anti-virus protection.

Any idea what I need to do to correct this situation??

I tried this, of course, but I get the same result; pictures are greyed out and pdf files show as "corrupted".

Thanks TTran for the link and its info. I tried compacting but it didn't help. I know now that it is an Outlook problem and not Windows &. I weht to my Hotmail account, attached a large file and sent it to my email account, which is a Pop3 account. The file went out without any trouble. I next went on to the web site for the POP3 account and the file opened without problem. Next I went to Outlook where I usually read the mail from this POP3 account and it took forever to down load it. Once downloaded it reported that it could not open the file because the file was corrupted. The same happened when trying to send a large file from Outlook; it remained in the Out Box. However sending the same file from the POP3 site was no problem. I've read everything I can find to see if there is some area of Outlook that indicates a maximum file size to send or receive. I haven't found that info. If you know if there is such a place please let me know. O, BTW, I have made sure the firewall and virus software were off when sending and receiving....still no help.

Outlook itself (Office, in fact) doesn't have a limit to how large an attachment you can send, but your network will. Many networks are throttled to 5MB. You can ask to have that increased, but the recipient may have a problem downloading the email at their end.

Thanks Druid. These files are way under 5MB. Most are just over 100K.