Yes the file ../libraries/gantry/core/renderers/gantrymodulesrenderer.class.php does exist on the server
the referenced line 60 in the error has the following code$modules = JModuleHelper::getModules($position);
I'm not following your reference to correcting the base directory. I did remove all of the server related information in the error leaving only the directory information following the httpdocs directory.
I'm up to date using Gantry 4.1.12 and joomla 2.5.11. I'll try reinstalling, but I doubt it will change anything since I have records of this error going back to Jan 19.