I was working on a asp.net project and while configuring email, I entered SMTP settings in web.config like this …

<System.net>
<mailSettings>
<smtp from=”xx@xx.xx”>
<network host=”xx.xx.com” port=”25″
username=”xx@xx.com”
password=”xx”
defaultCredentials=”false” />
</smtp>
</mailSettings>
</System.net>

All looked correct. But when I tried to access the site I got this error

“Parser Error Message: Unrecognized configuration section System.net.”

Now why was that? After a little research I discovered that “S” in <System.net> should be in small. If not you give this misleading error.

So the fix was to use <system.net> </system.net> instead.

After further research I fould that actually attributes in web.config are case sensitive. More details on this are can be found here.