Found the problem
When you navigate to certain pages in the admin section, is does a rewrite rule for things like:
https://websitename.com/admin/log/loglist?loglevelid=0&availableloglevels=system.collections.generic.list%601%5bsystem.web.mvc.selectlistitem%5d&log-grid-size=15
to
https://websitename.com/admin/log/list
I used the default rule provided with IIS 7 to make all urls lower case:
<rule name="LowerCaseRule1" stopProcessing="true">
<match url="[A-Z]" ignoreCase="false" />
<action type="Redirect" url="{ToLower:{URL}}" />
</rule>
When I removed this rule from web.config the admin section started working normally.