What is your firewall /antivirus-protection? Could it be interfering by trying to scan your outgoing mail?

Open Tbird and Tools/Error console Clear all, close Error Console. Try to send with attachment, (NOT a zero-size file). Reopen Error Console, what does it say?

I have 3 PCs in the same location all are protected with trendmicro, windows firewall and a hardware firewall, all are having the same settings and only one PC is having this Problem when I open tools I can't see the error console in the submenu

You can also use Ctrl+Shift+J to open error console

I cleared the error console and tried to send again with a non zero attachment mail was not sent and no errors in the error console

What's the difference between your PC's ? Have you tried running T-bird without add-ons enabled?

• Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled".

If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.

• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.