this message does not comply with required standards

I have Norton Internet Security 2010. When I try to send an email using Thunderbird with a link to this site:

 

http://click.bsftransmit28.com/ViewInBrowser.aspx?pubids=374|0110|679036&digest=RZ7YdH7Y5KNHtdAyDll63Q

 

I get an error message

 

"This message does not comply with required standards"

 

I get this even if I paste the link as a simple text string. My security history says the severity of this is "High", but gives no information about what the problem actually is. Can someone enlighten me?

 

Thanks

Richard