Outlook 2010 - Intermittent issues forwarding emails

Question

I have 2 users that will occasionally not be able to forward emails, when they click Send nothing happens.

This only happens when forwarding an email with an attachment, but not every time, 1 of the users having this issue forwards about 20 emails a day w/ attachments, but has the issue with one or two emails a week.

The recipient's email address is correct, starting a new email with all the same details will send.

While the email that won't send is still open I can successfully send other emails to other recipients.

In the application event log on the desktop
Event ID 27
Source Outlook
"The operation failed"

I see nothing wrong on the Exchange server.

Environment:
Outlook 2010 - cached mode enabled Windows 7 x86
Exchange 2007
Everything is fully patched.

Answer 1

Check the email and remove images. Try sending again. It should send after all images are removed.

Answer 2

I've seen a number of strange errors people get if they have upgraded the same Outlook PST file to 2010 from 2003 or 2007. The problem for them has been that they have Personal Contacts in their address book for some people who are also present in the Global Address Book, and for some reason this confuses Outlook 2010. Have your users check for and remove any entries in Personal Contacts or Recent Contacts for recipients of the files they're forwarding.

I would also be curious if the error happens through Outlook Web Access as well as the Outlook client.