My extension fails to install with status = -403 and -156

I'm struggling with getting my extension to install using ExManRoot. It's an extension for Premiere Pro CC 2015, and is meant to be compatible with version 9.0 and upwards.

Here is my manifest:

<?xml version="1.0" encoding="UTF-8"?>
<ExtensionManifest Version="5.0" ExtensionBundleId="com.thedinermusic.thediner" ExtensionBundleVersion="1.0.0"
  ExtensionBundleName="The Diner" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <ExtensionList>
  <Extension Id="com.thedinermusic.thediner" Version="1.0" />
  </ExtensionList>
  <ExecutionEnvironment>
  <HostList>
            <Host Name="PPRO" Version="[9.0,10.9]" />
  </HostList>
  <LocaleList>
  <Locale Code="All" />
  </LocaleList>
  <RequiredRuntimeList>
  <RequiredRuntime Name="CSXS" Version="6.0" />
  </RequiredRuntimeList>
  </ExecutionEnvironment>
  <DispatchInfoList>
  <Extension Id="com.thedinermusic.thediner">
  <DispatchInfo >
  <Resources>
  <MainPath>./index.html</MainPath>
  <ScriptPath>./jsx/import.jsx</ScriptPath>
                    <CEFCommandLine>
                        <Parameter>--enable-nodejs</Parameter>
                    </CEFCommandLine>
  </Resources>
  <Lifecycle>
  <AutoVisible>true</AutoVisible>
  </Lifecycle>
  <UI>
  <Type>Panel</Type>
  <Menu>The Diner</Menu>
  <Geometry>
  <Size>
                            <Height>420</Height>
  <Width>620</Width>
  </Size>
  </Geometry>
  <Icons>
  <Icon Type="Normal">./icons/dinericon.png</Icon>
  <Icon Type="RollOver">./icons/dinericon.png</Icon>
  <Icon Type="Disabled">./icons/dinericon.png</Icon>
  <Icon Type="DarkNormal">./icons/dinericon.png</Icon>
  <Icon Type="DarkRollOver">./icons/dinericon.png</Icon>
  </Icons>
  </UI>
  </DispatchInfo>
  </Extension>
  </DispatchInfoList>
</ExtensionManifest>

I used ZXPSignCmd (following these instructions​) to sign and package my extension into a ZXP file. I then attempted to install the package using ExManRoot, but got the error: "Failed to install, status = -403!"

Thinking it had to do with the fact that I hadn't set an install location for the ZXP, I tried uploading the ZXP file I just made to my developer portal using the online packager, with the following settings:

I then downloaded the ZXP file it generated through the developer portal, and attempted the install again. This time I got the error: "Failed to install, status = -156!"

Can someone tell me what these errors mean? No amount of Googling has led me to an explanation as to what status codes 403 and 156 are.

My first thought is that, as you can see in my screenshot, the online package automatically downcases the install location. I entered $adobecommon/CEP/extensions in the "custom location" dialogue, but it changes it to @adobecommon/cep/extensions. I believe this is an issue on Mac due to files and folders being case-sensitive (I'm testing on a Mac running Yosemite). Perhaps that's what's going on? If so, how can I force it to use the proper case?

I'm at a total loss here. Been trying to package/submit this extension for months now. Anyone who can help me get this damn thing accepted by the review process will officially be my best friend for life.