Probably Houdini installed the current license that you are using, which is a plain Apprentice (non-HD). This kind of license imposes some restrictions (resolution, watermark, export types) and has to be renewed every month.
Once you install (redeem) your HD license, Houdini will use that license. It does not expire and removes some restrictions.
There is a bug in the installer that does not set the file permissions correctly. This prevents the License Administrator from saving the HD license to this file and therefore the login window is grayed out.
To fix it, just set the write permissions on the licenses.local file in /Library/Preferences/sesi/ directory.
For some more info please see the Local Licensing FAQs:
http://www.sidefx.com/index.php?option=com_content&task=view&id=1283&Itemid=273 [
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