Are you sure you used the correct mojoPortal package for your version of .NET?
When did you download version 2.3.7.6? I patched it to fix a problem in Web.config so it was updated after the initial release.
You should make sure the new Web.config file has this:
<staticContent>
<!--
<clientCache httpExpires="Sun, 29 Mar 2020 00:00:00 GMT" cacheControlMode="UseExpires" />
-->
<!-- http://madskristensen.net/post/Prepare-webconfig-for-HTML5-and-CSS3.aspx -->
<remove fileExtension=".mp4"/>
<remove fileExtension=".m4v"/>
<remove fileExtension=".ogg"/>
<remove fileExtension=".ogv"/>
<remove fileExtension=".webm"/>
<remove fileExtension=".oga"/>
<remove fileExtension=".spx"/>
<remove fileExtension=".eot" />
<remove fileExtension=".otf" />
<remove fileExtension=".woff" />
<remove fileExtension=".svg" />
<remove fileExtension=".svgz" />
<mimeMap fileExtension=".mp4" mimeType="video/mp4" />
<mimeMap fileExtension=".m4v" mimeType="video/m4v" />
<mimeMap fileExtension=".ogg" mimeType="video/ogg" />
<mimeMap fileExtension=".ogv" mimeType="video/ogg" />
<mimeMap fileExtension=".webm" mimeType="video/webm" />
<mimeMap fileExtension=".oga" mimeType="audio/ogg" />
<mimeMap fileExtension=".spx" mimeType="audio/ogg" />
<mimeMap fileExtension=".svg" mimeType="images/svg+xml" />
<mimeMap fileExtension=".svgz" mimeType="images/svg+xml" />
<mimeMap fileExtension=".eot" mimeType="application/vnd.ms-fontobject" />
<mimeMap fileExtension=".otf" mimeType="font/otf" />
<mimeMap fileExtension=".woff" mimeType="font/x-woff" />
</staticContent>
Hope that helps,
Joe