In CB 1.7/Joomla 1.7 the mod_cblogin (and moderator/online) module manifests are missing the client attribute. The installer assumes that the client is 'site', which is ok. But, in \libraries\joomla\installer\adapters\module.php around line 75 we have the following code:
constant('JPATH_' . strtoupper($client))
Since $client is empty, the constant function tries to evaluate "JPATH_" and issues a warning, when the code is run in a debugger. (If it's run outside of a debugger, you see nothing.)
The problem here is that the language files wouldn't be loaded. I haven't checked yet to see if there are actually any language files affected by this.