Mac Mail Button Funtions Not Working; "Reply, Forward, New"?

Problem:

Recently the buttons in my Mail program seemed to have stopped working. My "Get Mail" button works properly and retrieves mail as it should. However, I cannot "Reply, Forward, or compose a "New" message. The buttons change color as I hover over them and click on them but nothing happens. Has anyone experienced this problem before or aware of any possible fixes?

I get a console error as follows upon clicking on the "New" mail button:

2010-06-12 23:09:44.761 Mail[443] * -[NSKeyedUnarchiver initForReadingWithData:]: incomprehensible archive (0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0)

KNOWNS:

I am not aware of making any changes that could have effected this functionality. I have tried numerous fixes:

Disk Utility: repaired permissions
AppleJack AUTO: system clean
plist file: moved to desktop
accounts: tried deleting and creating fresh email accounts in preferences
file scan: viruses etc
users: logged in as a different user (no luck)

I have googled around and looked through the forums with no luck as of yet. I found info on possibly downloading 3rd party software and installing ONLY the MAIL program from the OS install disk as a re-install but was holding out on this as a last resort; unless it is the only option as of now.

I want to say I remember this happening either to myself or on my brothers computer; where a certain attachment in an email was glitching the mail program; but I cannot remember exactly if this was the problem. I searched through my emails around the time of this issue but didn't find anything out of the ordinary as far as attachments.

I have been using Thunderbird which is working alright but I do like my Apple Mail. And I get annoyed when I can find a fix for something in particular. 🙂 I'd like to get my system back to normal.

Any help or suggestions would be much appreciated.

Thanks in advance!

MG