Working out of my element here ... ie, don't run 'Wonder' ... but can Google! ;)
http://www.webtrenches.com/post.cfm/iis7-file-upload-size-limits
article suggest there are two places for settings ...
there is an alternate solution that can be enabled at the site level rather than server-wide.
<system.webServer>
<security>
<requestFiltering>
<requestLimits maxAllowedContentLength="524288000"/>
</requestFiltering>
</security>
</system.webServer>
IIS7 article.
Was the service restarted after making changes?
And, think I'd set the value to something higher than 2 or 4 Gig ... Moodles only grow, they don't shrink. From what you've described, 30 Gig may not be in-appropriate.
Ok, now I am REALLY out of ideas for that platform! ;)
'spirit of sharing', Ken