Why is the “SendUsing” configuration value invalid for CDO.Message?

Getting CDO.Message.1 error ‘80040220’ The “SendUsing” configuration value is invalid. When sending mail?

In Classic ASP and perhaps others you might run across this, it was driving me insane as it worked fine on other sites, but not on this particular one. 

We were running our sites on Amazon AWS, Windows Server 2008 R2. 

Solution: 

In IIS 7: 

– Right click application pools 
– Find website 
– Right click and choose advanced settings 
– Change identity from ‘applicationpoolidentity’ to ‘Network Service’ 
– Try the code again 

This worked for me. It was mentioned on a form thread somewhere but didn’t seem to be the solution in that case.