Chrome ExtensionInstallSources policy

If you need to allow Chrome to install extensions from sites outside the chrome web store, you need to add the URL to the ExtensionInstallSources registry entry:

[In my case, I had to create Chrome\ExtensionInstallSources]

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Chrome\ExtensionInstallSources

Add a new string (REG_SZ) with the value 1 and data https://www.myurl.com/*.  For additional URL's, add a 2, 3, 4, etc..

Restart Chrome and attempt to re-install your extension.

http://www.chromium.org/administrators/policy-list-3#ExtensionInstallSources