I get the same error but it tries again and then it goes through. It has went through without fail to my wife and others, but not until after it gives a generic network failure message.

I am not sure what the limit is...

 

Mine sends video fine, but I have to reduce the quality to reduce file size. I just sent a quick 5 second video without a problem anyways.

Okay so I couldn't really send anything 800x480.
You can send a 5 second vid at 640x480.
You can send a 10 second vid at the other two lowest settings.

I believe the max file size is like 1.2m for mms. Not much.

... and for the generic network failure message, you need to shut off the failure notifications option in the stock messenger. That was the issue I experienced anyhow. Hope this helps.

 

Did you download the Quick Settings app? If so, that could be your problem. Read through this thread for the solution:
http://androidforums.com/support-tr...ure-texts-mms-culprit-quick-settings-app.html

 

There are multiple mms problems out there, they range from not downloading automaticaly to not being able to send like the op says. I have a trouble ticket open with Verizon and they told me it looks like a Verizon-HTC problem with the network. The tech told me that HTC would send out a software update to fix it but he has no time frame on when that would be. He said that the update probably wouldn't be 2.2 but just a minor update.

 

My phone wasnt letting me download 30kb images... but then 10 minutes later they would show up and numerous errors